Answer:77.5
Explanation:
The sum of all angles in a triangle must add up to 180.
180 - 39 = 141
This means that the other two points together must add up to 141, so we can divide 141 by 2 to get 70.5, this means both equations add up to 70.5
if you put 70.5 in one of them and solve (10x-7=70.5) then you get 77.5 for x