Given the function, f(x) = 5x + 15:
In order to find the value of x when f(x) = 30, substitute the value of the output into the function:
f(x) = 5x + 15
30 = 5x + 15
Subtract 15 from both sides:
30 - 15 = 5x + 15 - 15
15 = 5x
Divide both sides by 5:
15/5 = 5x/5
x = 3
Therefore, the value of x when f(x) = 30 is 3, or f(3) = 30.
