Answer:
x = - 6
Step-by-step explanation:
given y varies directly with x, then the equation relating them is
y = kx ← k is the constant of variation
to find k, substitute y = - 21 , x = 7 into the equation
- 21 = 7k ( divide both sides by 7 )
- 3 = k
y = - 3x ← equation of variation
When y = 18 , then
18 = - 3x ( divide both sides by - 3 )
- 6 = x
