Use the properties of exterior angles of triangles to find angle b while angle a is 142.

38.

52.

92.

232.

Since the sum of the exterior angles of a triangle is always 360 degrees, we can use this property to find angle b.

Given that angle a is 142 degrees, we can find the exterior angle at that vertex by subtracting it from 180 degrees (the sum of the interior and exterior angles at a vertex):
180 - 142 = 38 degrees

Since angle b is the exterior angle at the same vertex, angle b is also 38 degrees.

Therefore, the value of angle b is 38 degrees.