#### Answer

The answer is 17

#### Work Step by Step

Given the Ratios
$ \frac{12}{b} = \frac{36}{51} $
Cross Multiply
$12\times51 = b\times36 $
Simplify left side by multiplying 12 and 51
$ 612 = 36b $
Divide both sides by 36
$ \frac{612}{36} = \frac{36b}{36} $
b= 17
Therefore the solution is 17.