First we have to move b to one side of the equation and leave it there alone, here's how it's done:
[tex]\begin{gathered} \frac{5}{b}\text{ = }\frac{45}{36}\text{ } \\ \Rightarrow\text{ 5 = }\frac{45}{36}\text{ b} \end{gathered}[/tex]since 45/36 is multiplying b, we can send it to the other side dividing:
[tex]\begin{gathered} 5\text{ / (45/36) = b} \\ \Rightarrow\text{ b = 36/9 = 4} \end{gathered}[/tex]so b = 4
