Hello,
Let C the center of wheel.
P is the Carl's seat
A is the intercept of the horizontal line passing by A and the vertical line passing by P
In the right triangle PAC, sin 72°=AP/CP
==>[tex]AP=9*\sqrt{ \frac{10+2 \sqrt{5} }{4} } [/tex]≈8.5595....
The height of Carl's seat
is 11-8.5595...=2.440491...(m)