Final answer:
The function f(x) varies directly with x and can be expressed as f(x) = kx. By finding the value of k using the given information, we can find f(x) when x = 4.
Step-by-step explanation:
The function f(x) varies directly with x, which means that as x increases, f(x) also increases proportionally. We can express this relationship using the formula f(x) = kx, where k is the constant of variation.
Given that f(x) = 90 when x = 35, we can substitute these values into the equation to find the value of k. So, 90 = k * 35. Solving for k, we get k = 90/35 = 2.5714.
To find f(x) when x = 4, we can substitute the value of x into the equation: f(4) = 2.5714 * 4 = 10.2856.