Final answer:
To find the value of f(x) when x = 4 in a direct variation equation, we need to determine the constant of variation. Using the given equation and the given value of f(x) when x = 35, we can find the constant of variation and then substitute x = 4 to find f(x).
Step-by-step explanation:
To find the value of f(x) when x = 4, we first need to determine the constant of variation. Since f(x) varies directly with x, we can write the equation as f(x) = kx, where k is the constant of variation. To find k, we can use the given information f(35) = 90. Substitute this into the equation: 90 = k * 35. Solve for k: k = 90/35 = 2.5714 (rounded to four decimal places).
Now that we have the value of k, we can substitute x = 4 into the equation to find f(x): f(4) = 2.5714 * 4 = 10.2856 (rounded to four decimal places).