Answer:
x = 15
Step-by-step explanation:
Create and solve an equation of ratios. We can do this because the smaller triangle and the larger one are similar.
x 5 + x
------- = -----------
9 9 + 3
Cross-multiplying, we get 12x = 45 + 9x,
which simplifies to 3x = 45
Solving for x, we get x = 15
