recall that a flat-line is always 180°, so the 110° angle is just a supplementary angle, and her sibling is the angle in the triangle, check the picture below.
if you notice the tickmarks on those sides, that means they're equal, that means is an isosceles triangle, or with two equal sides, so the 70° angle is the vertex angle, and the other two angles are just two twins, 180 - 70 = 110, split that equally to the twins, and you get that, check the picture.
what's is "x"? well, "x" is just a supplementary angle of the one inside the triangle, thus 180 - 55.