There are special properties to certain right triangles.
A 3-4-5 triangle will always be a right triangle. 9 divides into 3, and 15 divides into 5, so you can use ratios to find b.
Since 9 divides into 3, we will use this to set up proportions for the missing value:
[tex] \frac{9}{3} = \frac{b}{4} [/tex]
Cross multiply the fractions.
[tex]3b = 36[/tex]
Divide both sides by 3.
[tex]b = 12[/tex]
The missing value is 12.
