Answer:
y = 2x
Step-by-step explanation:
since x and y vary directly then the equation is
y = kx ← k is the constant of variation
to find k use the given condition y = 18 when x = 9
k = [tex]\frac{y}{x}[/tex] = [tex]\frac{18}{9}[/tex] = 2, hence
y = 2x ← is the equation relating x and y
