Problem $22.$ Air flows into a $20-$meter section of a commercial steel rectangular duct with a cross$-$sectional area of $15$ cm by $20$ cm $,$ as shown. The air is at $1$ atmosphere and $35C,$ moving at an average speed of $7\frac{m}{s}.$ Ignoring entrance effects, calculate the power required by the fan to compensate for the pressure losses in this duct segment.

$($a$)$

$2$ W

$($b$)4$ W

$($c$)$

$6$ W

$($d$)7$ W

$($e$)$ None of these.