Answer:
h = 4.2
Explanation:
The large triangle beginning on the left has a height of 9. The small triangle has an unknown height of h almost in the middle of the of the base.
You can set up a proportion
9/h = 15/7 Cross multiply
15h = 9*7 Combine the right
15h = 63 Divide both sides by 15
15h/15 = 63/15
h = 4.2