## Calculus: Early Transcendentals 8th Edition

$140 \frac{cm^{2}}{s}$
Use the area of the rectangle: $(A = lw)$ $\frac{dA}{dt} = \frac{dl}{dt}w + l\frac{dw}{dt}$ $\frac{dA}{dt} = 8(10) + 20(3)$ $\frac{dA}{dt} = 80 + 60$ $\frac{dA}{dt} = 140 \frac{cm^{2}}{s}$