Answer:
y = 7.5
Explanation:
Given y varies directly with x then the equation relating them is
y = kx ← k is the constant of variation
To find k use the condition y = 10 when x = 20
10 = 20k ( divide both sides by 20 )
= k
y =
x ← equation of variation
When x = 15 , then
y =
× 15 =
= 7.5