Solve the Problem $\mathrm { f } ( \mathrm { t } ) = 189 - 32 \mathrm { t } \mathrm { ft } / \mathrm { sec }$

Multiple Choice

Solve the problem.
-A toy rocket is launched straight up from level ground. Its velocity function is $\mathrm { f } ( \mathrm { t } ) = 189 - 32 \mathrm { t } \mathrm { ft } / \mathrm { sec }$ , where $\mathrm { t }$ is the number of seconds after launch. At what time does the rocket reach its maximum height?

A) $6.23 \mathrm { sec }$
B) $5.72 \mathrm { sec }$
C) $5.91 \mathrm { sec }$
D) $11.81 \mathrm { sec }$