Answer:
66
Step-by-step explanation:
The sum of all of the angles in a triangle is 180. So all three angles would add up to 180:
(a + 21) + 57 + (a - 30) = 180
Combine like terms:
2a + 48 = 180
2a = 132
a = 66
a+21+57+a-30=180(angle of triangle)
2a+48=180
2a=180-48
2a=132
a=132/2
a=66
then,a+21=66+21 =87
a-30=66-30 =36
I think this is the answer
