The problem does not state the type of variation. If it's a direct variation, then it's like proportion problems.
Assuming it's a direct variation:
y varies directly with x. If y = -18 when x = 9, find y when x = 7.
y = kx
-18 = k (9)
-18/9 = k (9)/9
-2 = k, constant of direct variation.
To solve for y, use the constant of variation, -2 when x = 7
y = -2(7)
y = -14, final answer.
Assuming it's an inverse variation:
y varies inversely with x. If y = -18 when x = 9, find y when x=7.
y = k/x
-18 = k/9
k = (9) (-18)
k = -162, the constant of inverse variation
Using the constant -162 for y = ? when x = 7
y = k/x
y = -162/7
y = -162/7 or -23 1/7
See the difference in y values?
