Problem $1[2$ points$]$

$($a$)$ An unswept airfoil at a given angle of attack has a critical Mach number of $0\mathrm{.}75.$ Find the sweep angle that is required to obtain a critical Mach number of $0\mathrm{.}85$ at the same angle of attack.

$($b$)$ You see a UAV with a delta wing that is swept back at an angle of $53.$ Determine what Mach number it could fly at and still maintain subsonic flow normal to the leading edge.