What is the length of a 9 meter pool with 90 square meters

10 meters. L x W = Area. The length is 9, so the width has to be ten to get an area of 90 square meters.

Area of a rectangle can be represented as L x W = A squared.
Knowing only one side and the final area calculation and realizing that the commutative property says that it doesn't matter what order numbers are multiplied in we can write an equation that represents the rectangle using the variable x to represent what we don't know.
9x= 90
Solve the equation for x!