Solve the Problem $40 \mathrm { ft }$ Wide and the Canal Is

Multiple Choice

Solve the problem.
-A cross-section of an irrigation canal is a parabola. If the surface of the water is $40 \mathrm { ft }$ wide and the canal is $7 \mathrm { ft }$ deep at the center, how deep is it $10 \mathrm { ft }$ from the edge?

A) $1.8 \mathrm { ft }$
B) $3.1 \mathrm { ft }$
C) $3.9 \mathrm { ft }$
D) $5.2 \mathrm { ft }$