Question

the function f(x) varies directly with x and f(x)=3 when x=12 what is the value of f(x) when x=40

Answer 1

It says f(x) varies directly which means that x and f(x) relate to each other by multiplication. f(x)=nx where n is a number that is constant. That is what you need to solve for first. For example, 3=12n. that means n=1/4. So then you use this to plug into the next equation. f(x)=(1/4)x(40) so f(x) will be 10