Solve the Problem $t$ Minutes After the Pool Has Started to Drain Is

Solve the problem.
-The number of gallons of water in a swimming pool $t$ minutes after the pool has started to drain is $Q ( t ) = 50 ( 20 - x ) ^ { 2 }$ . How fast is the water running out at the end of 11 minutes?

A) $450 \mathrm { gal } / \mathrm { min }$
B) $4050 \mathrm { gal } / \mathrm { min }$
C) $2025 \mathrm { gal } / \mathrm { min }$
D) $900 \mathrm { gal } / \mathrm { min }$