The sum of all interior angles in a triangle is 180°.
the angles in this triangle are on a 2:2:4, we know if we add all those three angles, we'd end up with 180°, therefore then 180 is on a 2:2:4 ratio.
in other words, 180 divided by (2+2+4) gives us 22.5°.
now, we know one angle takes 2 of those 22.5, so is 22.5+22.5 or 45°.
the other angle takes the same 2 of those, so is also 45°.
and the largest one takes 4 of those, so is 22.5(4) or 90°.
now, what's the exterior angle to a 90° angle? check the picture below.