First, you find the angle inside the triangle on the bottom right. You can do this using the 123°, because angles on a straight line add up to make 180°.
180°-123° = 57°
Angles in a triangle also add up to make 180°. You now have two angles, so can therefore find the third by subtracting those two from 180°.
180°-(57°+42°) = 180°-99°= 81°
Now you can use the same rule as the start to find x (angles on a straight line add to 180°)
180°-81° is going to give you 99° because we have reversed the previous step. When you get more confident with this you can skip steps but for now it’s better to just write it all out.
So x = 99°
