Chapter P, Prerequisites - Section P.9 - Modeling with Equations - P.9 Exercises - Page 73: 67

$18 $ feet tall.

Using the volume formulas the equation for the volume: $r^2\pi(\frac{2x}{3})+\frac{1}{3}r^2\pi(\frac{x}{3})=1400\pi\\10^2\pi(\frac{2x}{3})+\frac{1}{3}10^2\pi(\frac{x}{3})=1400\pi\\600x+100x=12600\\x=18$ Thus it is $18 $ feet tall.