Y=5x-25, the output is - 25 what's the input

In the equation y = 5x - 25, x is the input and y is the output. You know this because you start with some x value, apply some operations, and you get the answer y. So if - 25 is the output, then y=-25. To find the input, just solve for x:

y=5x-25

-25=5x-25

0=5x

x=0

So the input is 0.

Y = 5x - 25

output = - 25

-25 = 5x - 25

5x = - 25 + 25

5x = 0

x = 0

Answer: Input = 0