tolong dijawab plissss

a. 3 x - 45 = x + 23
3x - x = 23 + 45
2x = 68
x = 34 ←


b. BCF = 180˚ - ABC
= 180˚ - (3x - 45)
= 180 - (3.34 - 45)
= 180 - 57
= 123˚ ←