The angels 60, a, and 55 are supplementary, meaning they add up to 180 degrees.
Therefore we have
Solving for a gives us
Now, we know that the sum of angles in a triangle is 180 degrees; therefore,
since a = 65, we have
solving for b gives us
The angle c is opposite the angle b; therefore, it is
Angles d and 15 are complementary meaning they add up to 90; therefore, we have