Required information

NOTE: This is a multi$-$part question. Once an answer is submitted, you will be unable to return to this part. Consider three forces A$,$ B$,$ and C$,$ where A $180N,B=155N,$ and $C=240N.$ A collar that can slide on a vertical rod is subjected to the three forces shown.

Determine the required value of $a$ if the resultant of the three forces is to be horizontal.

The required value of a for the resultant of the three forces to be horizontal is