Answer:
x = 7 cm
Step-by-step explanation:
The perimeter of the given triangle:
P = (2x + 1) + (x + 2) + (3x - 9) and P = 36 cm.
Therefore we have the equation:
2x + 1 + x + 2 + 3x - 9 = 36 combine like terms
(2x + x + 3x) + (1 + 2 - 9) = 36
6x - 6 = 36 add 6 to both sides
6x = 42 divide both sides by 6
x = 7
