Answer:
3

Explanation:
Find 'c' first by using the Altitutude Rule:
4/c = c/9
cross-multiply to get:
c = 
 or 6
 or 6
Now you can find 'a' by using the Pythagorean Theorem:
4² + 6² = a²
a = 

Now you can find 'b' by using the Pythagorean Theorem:
(
 )² + b² = (9+4)²
)² + b² = (9+4)²
52 + b² = 169
b² = 

b = 
 =
 = 



b = 3
