Answer: x=9
Explanation: All 3 angles of a triangle add up to 180, so basically the equation is (3x-5)+(7x+5)+90=180.
Then you add your like terms, so 3x+ 7x=10x and -5+5=0, which cancels out. Now we have 10x+90=180, we subtract the 90 from 180 to see what 10x is equal to and we get 90. So 10x=90. We divide 10 from 90 and we get the value of X, which is 9.