Mr. Williamson bought 4 boxes of chewy granola bars and 5 boxes of crunchy granola bars. Each box contained the same number of granola bars. He took all 72 granola bars to the class picnic. How many granola bars were in each box? Let x represent the number of granola bars in each box.

Step 1: Write an equation.

Step 2: Identify and combine like terms.

Step 3: Use the properties of equality and inverse operations to solve the equation.