Answer:
x = 5
Explanation:
so since the triangles are congruent, you need to set them equal to each other and combine like terms.
9x + 3 = 6x + 18
subtract 3 to get the numbers all on one side
9x = 6x + 15
subtract 6 to get all the variables on the left side
3x = 15
divide
x = 5