Let the total number of cans be x and the total number of tennis balls be y,
Since increasing the total number of cans causes the total number of tennis balls to increase too, x and y is direct in proportion.
Let the constant be k,
y = kx
45 = k9
k = 45/9
= 5
The constant of the proportionality for this situation is 5.
The answer is $675. You find 5 percent of 4500 and then multiply by 3.
