His Angle Formation, My early Dismissal.

On a hot Saturday morning we have college cadet formation. We've been dried under the sun for an hour with 45 angle feet degree, erected hands back, and eye looking 180 degree sharp. After an hour he rest us for 30 minutes. 15 minutes for water therapy and necessity and another minutes will be preparation for drill. As we got back prior to drill preparation, our mentor gave us the situation mathematically. According to him," If anyone can answer correctly will be dismiss early". He said,"Considering that one of my feet is x-axis and the other one forms a line of 2y-9x-18. Compute the degree of my feet formation between?" After 10 minutes I found the angle of his feet formation and I was dismiss. How did I solve it?