The angles of a triangle always add up to degrees. One side is double the other, so then , and the third angle is double of the first angle. This is slightly ambiguous as to what the first angle is, but I read it as being , so .

Let's add up all the angles to equal one hundred and eighty degrees. .

Write everything in the form of one variable. It so happens that B is the easiest.

Solve for A and C.