Answer:
90
Explanation:
1. The other angle marked with one arc must also be 43 deg.
2. The two angles put together make an angle of 86 deg.
3. In a parallelogram, the angle at lower right and the angle at upper right are supplementary (they add up to 180 deg.). The upper right angle is 180 - 86 = 94 deg.
4. The angle at lower left is the same, 94 deg.
5. The angles marked with two arcs are half of 94 deg. = 47 deg.
6. Now you have two out of three angles in the triangle. All three angles add up to 180 deg. so the measure of angle 1 is 180 - 47 - 43 = 90 degrees.