Answer:
x = 11.4
Explanation:
The sum of the angles of any triangle must add up to 180°. Since we have the expressions for each angle: 5x, 8x, and (2x +9), we can solve for the variable of 'x' by adding the expressions together and setting them equal to 180:
5x + 8x + (2x +9) = 180
Combine like terms: 15x + 9 = 180
Use inverse operations: 15x + 9 - 9 = 180 - 9
15x = 171 or x = 11.4
Check: 5(11.4) + 8(11.4) + 2(11.4) + 9 = 57 + 91.2 + 22.8 + 9 = 180