The answer is B, 57 degrees. You can tell angle C is 57 degrees since 180-123 is 57 and both angles add up to 180 on a straight line. Then since the lines are parallel, angle a is 55 degrees because of alternate interior angle theorem. Then, a triangle’s angles add up to 180 so to figure out angle d, you do: 180- (55 + 57) which gives you 68. Since 55 + angle b + angle d = 180, you have to do 180 - (68+55) = 57 degrees. Hope this helps!
