Answer:
x = 6 when y = 18
Explanation:
"y varies directly with x" is represented by y ∝ x and translates to the equation y = kx
where k is a constant known as the constant of proportionality
Given y = 15, when x =5 we can determine k
15 = k · 5
k = 3
So the proportionality equation is
y = 3x
When y = 18,
18 = 3x
x = 18/3 = 6