“Determine the values for angle a, b, c and d in the diagram below” Help me with this question please

Lets start with d, since its all alone, take 180 - 58 = d, which is 122 = d, next c, 180 - 48 - 58 = c, which is 74 = c, next a, since d is 122, 180 - 122 = a because d + a = 180, a = 58, a + b + c = 180 so, 180 - 58 - 74 = b, b = 48

A=58

B=48

C=74

D=122

f(x) = x^3 -2x^2 -3x

x( x^2 -2x-3)

x( x^2 +x -3x -3)

x( x(x+1) -3(x+1))

x( x-3)( x+1)

so zeroes are 0, 3,-1

its (2) option