Geometry: Common Core (15th Edition)

$A=162\text{ in}^2$
The formula for the area of a rectangle is $A=bh$. In order to use this formula, however, we must have the same units for the base and the height. Since there are $12$ inches in a foot, we multiply the number of feet of the base by $12$ to get the number of inches of the base: $$2.25\text{ ft}\times\frac{12\text{ in}}{1\text{ ft}}=27\text{ in}$$We now plug in the values for the base and the height into the formula and simplify: $$A=27\text{ in}(6\text{ in})=162\text{ in}^2$$