A function follows the rule y = - 75 - 5x. When the function's output is 25, the equation is 25 = - 75 - 5x.

What is the function input when the output is 25?

All you need to do is solve for X. You simply isolate the variable by adding 75 to 25, which will yield 100. To get rid of the 2x you divide both sides by two, and reach the conclusion that X=50.