Chapter 1 - Tools of Geometry - 1-8 Perimeter, Circumference, and Area - Practice and Problem-Solving Exercises - Page 66: 43

$96\ cm^2$

Use the formula for the perimeter of a rectangle to find the height. $P=2b+2h$ $40=2(12)+2h$ $40=24+2h$ $40-24=24+2h-24$ $16=2h$ $16\div2=2h\div2$ $8=h$ Use the formula for the area of a rectangle. $A=bh$ $A=(12)(8)$ $A=96$