∠c and ∠d are vertical angles with m∠c=−2x+90 and m∠d=x−30 . what is m∠d ?

∠C = ∠ D (vertical angles

C= -2x + 90
D= x-30

Since C = D , Then -2x + 90 = x-30

-2x - x = - 30 - 90

-3x = -120

3x = 120 and x = 40°. Now replace x by 40 in any of the equality, say :
D = x-30 ; D = 40 - 30 and D = 10°

I’d say letter a..

20y5 times 2 is 1010 times -2 is -20, plus y