The exterior angles of any polygon add up to 360. (A square has four sides, each has an exterior angle of 90 - an octagon has eight sides, each side has an exterior angle of 45 (8 x 45 = 360))
You know that four of the five sides of your polygon has exterior angles of 50, making a total of 200 (4 x 50). The final angle needs to add up to 360 so is 360 - 200 = 160
