So to solve a,
You already have the first two answers which are 65 and 90. Since a tríenle always has to equal 180 you just add 65 and 90 and the subtract that number by 180 and that’s your other missing angle.
Both triangles are identical so you just have to insert the answers from the right triangle onto the left triangle.
A is the only one that I knew how to solve, sorry