Answer:

Step-by-step explanation:
A straight angle is equal to 180° degrees. Since both 9x +4 and 3x -18 is supplementary then I can make this claim below

All we have to do now is to solve for x

Answer:
x=5
Step-by-step explanation:
Since the triangles are similar we can use ratios to solve
4.5 7.5
---- = ------
3 x
Using cross products
4.5x = 3 * 7.5
4.5x = 22.5
Divide each side by 4.5
x = 22.5/4.5
x=5