Chapter 7 - Similarity - 7-1 Ratios and Proportions - Practice and Problem-Solving Exercises - Page 437: 29

$\frac{a}{3}$; Property of Proportions #2

You are given $\frac{a}{b}$=$\frac{3}{4}$ The second Property of Proportions states $\frac{a}{b}$=$\frac{c}{d}$ is equivalent to $\frac{a}{c}$=$\frac{b}{d}$ Switching the means gives you $\frac{a}{3}$=$\frac{b}{4}$