The angles of a triangle add up to 180 degrees
65 + 3x - 10 + 2x = 180
5x + 55 = 180
5x = 180 - 55
5x = 125
x = 125/5
x = 25 <====
m < B = 3x - 10 = 3(25) - 10 = 75 - 10 = 65 <== B is 65 degrees
m < C = 2x......= 2(25) = 50 <== C is 50
You have to do 3.14 times the diameter of the circle.
Subtract 76 on both sides:
2401 - 76 = 76 - 2x - 76
2325 = -2x
Divide both sides by -2:
-1162.5 = x