Answer:
y = 6
Step-by-step explanation:
Given that 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 = 3 when x = 9, then
k = [tex]\frac{y}{x}[/tex] = [tex]\frac{3}{9}[/tex] = [tex]\frac{1}{3}[/tex], thus
y = [tex]\frac{1}{3}[/tex] x ← equation of variation
When x = 18, then
y = [tex]\frac{1}{3}[/tex] × 18 = [tex]\frac{18}{3}[/tex] = 6
