Answer
The final speed of the crate is 14.9 m/s.
Work Step by Step
We can use work and energy to solve this question. Note that the initial kinetic energy is zero. The final kinetic energy is the sum of the positive work done by the pull $W_p$ and the negative work of friction $W_f$. Therefore,
$KE = W_p + W_f$
$\frac{1}{2}mv^2 = F_p\cdot (21.0~m) - F_f\cdot (10.0~m)$
$v^2 = \frac{(2)(225~N)(21.0~m)-(2)(36.0~kg)(9.80~m/s^2)(0.20)(10.0~m)}{36.0~kg}$
$v^2 = 223.3~m^2/s^2$
$v = \sqrt{223.3~m^2/s^2} = 14.9~m/s$
The final speed of the crate is 14.9 m/s.