Yes I originally thought 90 but then noticed the absence of a right angle sign. Also 60+40=100 which means the last angle should be 80. Making that perpendicular 100/80
You start from left, and calculate them 1 by 1, based on the angles that you already know. It is quite simple actually, you just have to know they always add up to 180 (within triangle, and when you โsplitโ the space over a straight line).