Answer:
y = - 54
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 = - 9 when x = 3 , then
- 9 = 3k ( divide both sides by 3 )
- 3 = k
y = - 3x ← equation of variation
When x = 18 , then
y = - 3 × 18 = - 54