At Ashley's Nursery, there are 12 rows of trees. In each row, there are 21 pine trees and 7 spruce trees. How many of each type of tree are there in all?

So what you have to do is:

To find the number of pine trees:

12 (because there are 12 rows) * 21 (as there are 21 pine trees in each row), so

12 * 21 = 252

There are 252 pine trees

You then repeat this process to find out how many spruce trees there are

So:

12 (the amount of rows) * 7 (there are 7 spruce trees in each row)

12 * 7 = 84

Number of pine trees = 252

Number of spruce trees = 84