In the last 4weeks, after mowing the front and back yards, you have accumulated 90pounds of grass in the trash. What is the rate of pounds per week?

First let's define what a rate is, we have is a coefficient that expresses the relationship between the quantity and the frequency of a phenomenon or a group of numbers.

In this case they ask us for the rate between pounds per week, therefore the coefficient is between the pounds there are, which are 90 and the number of weeks, which are 4, therefore it would be:

r = 90/4 = 22.5

That is, the rate is 22.5 pounds per week.