how do I solve this

Answer:
Step-by-step explanation:
Simplifying
f(x) = 800(0.85) * x
Multiply f * x
fx = 800(0.85) * x
Multiply 800 * 0.85
fx = 680x
Solving
fx = 680x
Solving for variable 'f'.
Move all terms containing f to the left, all other terms to the right.
Divide each side by 'x'.
f = 680
Simplifying
f = 680