In all cases, take into account that the sum of the interior angles of a triangle is equal to 180°. Then, for the first triangle you have:
2x + 2x + x = 180 simplify like terms left side
5x = 180 divide by 5 both sides
x = 180/5
x = 36
For the second triangle:
7x + 3x + 90 = 180 subtract 90 both sides
7x + 3x = 180 - 90 simplify like terms both sides
10x = 90 divide by 10 both sides
x = 90/10
x = 9
For the third triangle:
x + x + 2x = 180 simplify like terms left side
4x = 180 divide by 4 both sides
x = 180/4
x = 45