Answer:
x = 10
I used the Interior Angles of a Triangle Rule --The sum of all 3 interior angles in a triangle is always 180°.
(3x + 28) + (5x - 18) + 90° = 180°
Now i can get rid of the parentheses and combine like terms.
3x + 5x + 28 - 18 + 90 = 180
8x + 10 + 90 = 180
8x + 100 = 180
Then i subtract 100 from both sides to isolate x.
8x + 100 - 100 = 180 - 100
8x = 80
Then, i divide both sides by 8 to find x.
8x ÷ 8 = 80 ÷ 8
x = 10
