Answer:
y = 6 when x = 18
Step-by-step explanation:
The appropriate formula for this direct proportion is y = kx, where k is the constant of proportionality.
We know y = 3 when x = 9: 3 = k(9)
This yields k = 3/9, or k = 1/3
Then the formula is y = (1/3)x
and when x = 18, y = (1/3)(18) = 6
y = 6 when x = 18
