Graph of a proportional relationship
A proportional relationship can be written as
y = kx
Where k is a constant.
In the problem, the horizontal axis represents the time in minutes it takes for the sunshine cleaning service to vacuum a carpet's square yards of area, represented in the y-axis.
We know the service vacuums 8 square feet of carpet every 4 minutes. This means the point (4,8) must belong to the graph.
If the service works at a constant rate, then in 2 minutes (half the time) it would vacuum half the area of 4 square feet. This is the point (2,4).
The only graph that has both points and is a straight line passing through the origin is the graph marked with the letter B.