We will start with the angle that measures 57 degrees. This angle is supplementary to the one next to it coming off the straight line. 180 - 57 = 123.
The rule for quadrilaterals is that same side angles are supplementary, so the angle next to the 123-degree angle (to the immediate left of that angle 123) is 57. THAT 57-degree angle is supplementary to angle b, so angle b = 180 - 57 which is 123. So C is your answer.
