## Algebra: A Combined Approach (4th Edition)

$90$ horsepower
Let $h$ be the horsepower. Let $r$ be the number of revolutions per minute. Let $d$ be the diameter of the shaft. $h=krd^3$ $h=40; r=120; d=2$ $40=k(120)(2)^3$ $k=\frac{1}{24}$ $h=\frac{1}{24}rd^3$ $r=80; d=3$ $h=\frac{1}{24}(80)(3)^3$ $h=90$ horsepower