Apack of gum costs 75 cents. that is 3 cents less than three times what the pack cost 20 years ago. which equation could be used to find the cost of the gum 20 years ago?

The answer to your question is: .75 = 3x - .03

How to solve it:

x = the cost of a pack of gum twenty years ago

.75 =  3x - .03
+ .03      + .03

.78 = 3x
 / 3    / 3         

.26 = x

If a pack of gum now costs 75 cents, which is 3 cents less than three times what a pack would have cost 20 years ago, then a pack of gum would have cost 26 cents. 

Hello!
volume of sphere =4/3.pi.r^3