$2\mathrm{.}38$ Knowing that $=75,$ determine the resultant of the three forces shown.

$2\mathrm{.}39$ A collar that can slide on a vertical rod is subjected to the three forces shown. Determine $($a$)$ the required value of $a$ if the resultant of the three forces is to be horizontal, $($b$)$ the corresponding magnitude of the resultant.