hello
so what we can gather form the diagram given is that all the angles there will add up to 360°.
we can see that they have given one of the angles as 90° as indicated by the little square. so the first step to find x, we need to subtract 90 from 360.
360-90=270
now, we can form an equation to find x. we need to add the other two angles (x, 3x) and then make them equal to 270°.
3x+x=270
add like terms
4x=270
divide by 4
x=67.5°
hope this helps
have a nice day :)