The value of a is 85°
From the diagram :
- a + 57 + 2x = 180 __(1) (sum of angles in a triangle)
- a + 5x = 180 ___(2) (sum of angles on a straight line)
From (1)
a + 2x = 123
a + 5x = 180
subtract
2x - 5x = 123 - 180
-3x = -57
x = 19
a = 123 - 2x
a = 123 - 2(19)
a = 123 - 38
a = 85
Hence, the value of a is 85°