a. we know that cab is 35 degrees and b is 90 degrees. From this, and knowing that there are 180 degrees in a triangle, we can set up a simple equation.
180-90-35+ acb
b. so we know the measure of acb and acd will add to 180 and we also know acb from part a
180=acb+acd
c. We are given that D is 35 and B is 90. From this we know that 180-90-35 is angle A. We only want the cad part of angle A, but we know the other part cab. From this we know that
cab+cad=A