Please solve the problem . I am not able to solve it. Is there a deductive way to solve it?

sina+sin^2a = 1

=> sina=cos^2a
now squaring on both sides
cos^4a = sin^2a
cos^4a=1-cos^2a
=> cos^4a + cos^2a = 1
now cubing on both sides
cos^12a + 3 cos^10a + 3 cos^8a + cos^6a = 1
now comparing with given equation
a = 1  b=3 c=3 d=1
=> required answer = 3 + 3 +1 = 7