Water tank is being filled with water. Before water is pumped in, the water level in the tank is 12 inches high. After 20 minutes, the water level is 54 inches high. If t represents the time in minutes and h represents the water level, which of the following equations can be used to model this situation?
A. H = 42 + 12t
B. H = 2.1t - 12
C. H = 12t + 2.1
D. H = 2.1t + 12

let x and 400 - x be the two numbers.  

==> 0.80x + 0.85(400 - x) = 400 - 68 from the statement of the problem.  

< ==> 0.80x + 0.85(400 - x) = 400 - 68  

==> 340 - 0.05x = 332  

< ==> -0.05x = -8 ==> x = 160, the first number ==> 400 - x = 240, the second number.

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step-by-step explanation:

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add -60 to 120 which will result in : 2x+3y=180

then subtract 2x: 3y=-2x+180

lastly, divide by 2: y= -2/3x+60

hope this is the answer you're looking for: )