## Basic College Mathematics (10th Edition)

$x=6.5$
We can set the cross products of the given proportion equal to each other and then solve for the unknown variable. $7.8\times x=3.9\times13$ $7.8x=50.7$ Divide both sides by 7.8. $\frac{7.8x}{7.8}=\frac{50.7}{7.8}$ $x=6.5$