hello
so to find x, we need to use a rule.
the rule is: the exterior angle of a triangle is equal to the sum of the opposite interior angles.
so our exterior angle is xº, and the opposite interior angles are 53º and 45º.
we could set up a basic equation (although not completely necessary)
xº=53º+45º
xº=98º
hope this helps
have a nice day :)