Question

The function f(x) varies directly with x, and f(x)=45 when x=9 evaluate f(x) when x=3

a) 5
b) 9
c)15
d)27

Answer 1

f(x) is the same as y

9/45 = 3 / y
cross multiply
(9)(y) = (45)(3)
9y = 135
y = 135/9
y = 15 <==

Answer 2

the answer is -

c) 15