Question

What is the size of the angle at the top labeled A?

Answer 1

The answer is 40 degrees. (:

Answer 2

All triangles have 180°.

As you can see from this triangle, it is an isosceles triangle, because the two angles are the same (I can assume that the two sides are, as well).

As we have two exterior angles that are perpendicular, we can assume that:

$x + 110 = 180$

$x=70$

The interior angles is 70 degrees.

We have two interior angles that are the same, so it totals up to 140 degrees.

As mentioned, a triangle has 180 degrees.

Let's use logic.

$140 + x = 180$

$x= 40$

The angle measures exactly 40 degrees.