Answer: -60 = x
Explanation:
If the output value is -15, we need to do this equation.
-15 = (1/3)x + 5.
-5 -5
-20 = (1/3)x
x3 x 3
-60 = x.
Now, let's double-check our answer.
f(60) = (1/3)(-60) + 5
f(-60) = -20 + 5
f(-60) = -15.
This means that x = -60 is our correct answer.