Serena wants to determine the area of the lawn, the grass part of her front yard, using the information given in the diagram below. Serena knows that she needs to divide by 9 to change the units from square feet to square yards, so she writes the expression below to determine the area of the grass in square yards.
[48 (72 - 12) - 15] ÷ 9
What is the area of the lawn of Serena's front yard, in square yards?