The "zero" is:  " 2 " ;  or, write as:  " 2.92 " .
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       →   " t = 2 " ;  or, write as:  " t = 2.92 " .
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Step-by-step explanation:
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Letting assume that this given function is supposed to be written as:
 "distance as a function of time" ;  that is:
      d(t) = 70 - (2.4)t ;
 →  since distance, "d" is the dependent variable (cannot be "manipulated or controlled") and as such, belongs on the "y-axis"—as the "dependent variable" ;  whereas as time, "t" ; can be somewhat controlled (with respect to distance, at list as a starting point); and as such belongs on the "x-axis" as the "independent variable" .
Since no "specific units" are given to us in the problem for Either "distance" or "time" ; we shall use the term "units" to describe their values.
We have:
 d(t) = 70 - (2.4)t ;
Let us rearrange this:
70 - (2.4)t  ;  ↔
 =  70  +  (- 2.4)t  ;  ↔
 =  (-2.4)t  +  70 ;
And rewrite the function:
     →  d(t) = (-2.4)t + 70 ;
To find the "zero" ; or "zeros" ; of this function; set "d(t)" equal to "zero" ; that is; "0" ; and solve for  the value(s) for "t" when "d(t)" = 0 :
     →  0 = -2.4(t) + 70 ;  ↔
  Rewrite as:
     →  -2.4(t) + 70 = 0 ; Â
For simplicity; Â let us multiply Each side of the equation by "10" ;
to get rid of the decimal value:
  10*[ (-2.4)t) + 70 ] = 10 * [0] ;
From the left-hand side of the question:
Note the "distributive property" of multiplication:
  a(b + c) = ab + ac ;
As such:
  10* [-2.4(t) + 70 ] =
  [10* -2.4(t)] + [10 * 70] =
   -24t + 70 ;
From the "right-hand side" of the equation:
  10 * 0 = 0 .
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So; we rewrite the equation as:
 -24t + 70 = 0 ;
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Solve for " t " ; Â
 -24t + 70 = 0 ;
Subtract "70" from Each Side of the equation;
 -24t + 70 - 70 = 0 - 70 ; Â
to get:
 -24t = -70 ;
Now, let's multiply each side of the equation by "-1" ;
    to get rid of the "negative values" ;
 -1* (-24t) = -1(-70) ;
to get:
  24t = 70 ;
Now, let's divide Each Side of the equation by "24" ;
to isolate: Â "t" ; Â on one side of the equation; & to solve for "t" ;
  24t / 24 = 70/24 ;
to get: Â
     t = 70/24 ;
To simplify: Â either: Â
1)  use calculator:  70 ÷ 24 = 2.916666666 ;
               →  round to:  2.92 ;
               →  t ≈ 2.92 ;
 or:  " ;
→  write as simplified improper fraction:  " t = "
→  or:  write as mixed number:
      →  " = 35 ÷ 12 =
               2 R 11
           12 ⟌35
             - 24 Â
               1 1
    Â
      →  write as:  " 2 " ;
                                →  " t = 2 " .
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Hope this is helpful to you.
    Wishing you the best!
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