$6-8.$Please solve the problem except for the yellow mark.

A $20-$story office building has plan dimensions of $10060ft$ and is oriented at $45$ degrees to

a $20$ mph wind. All windows are fixed in place. There are double vestibule$-$type swinging doors

on the $60-$ft walls. The walls are tight$-$fitting curtain wall construction, and the doors have about

$\frac{1}{8}$ in$.$ cracks. $($a$)$ Compute the pressure differences for each wall due to wind and stack effect

for the first, fifth, fifteenth, and twentieth floors. Assume $t_i-t_o=40$ F$.($b$)$ Plot pressure dif$-$

ference versus height for each wall, and estimate which surfaces have infiltration and exfiltra$-$

tion. $($c$)$ Compute the total infiltration rate for the first floor, assuming $400$ people per hour per

door. $($d$)$ Compute the infiltration rate for the fifteenth floor. $($e$)$ Compute the infiltration rate

for the twentieth floor. Neglect any leakage through the roof.