Answer:
x = 9
Step-by-step explanation:
A triangle's interior angles must add up to 180, and with one angle labeled as a right angle, we know that the two remaining angles must add up to 90.
So,
(3x - 5) + (7x + 5) = 90
3x + 7x - 5 + 5 = 90
10x = 90
x = 9
