Answer: 121°
The first to solving this problem is to first find the missing angle in the triangle.
Three angles in a triangle have to add up to 180°
We are given the angles 87° and 34°, so now let's add the two given angles
87° + 34° = 121°
Now let's take 180° and subtract it from 121° to get the missing angle in the triangle
180°-121°=59°
Now we know the missing angle is 59°, we can notice that the angle 59° is also on a straight line and two angles on a straight line must add up to 180°
So let's now subtract 180° from 59°
180°-59°=121°
