Answer
$x=560\ ft$
Work Step by Step
$\frac{28}{x}=\frac{5}{100}$ $\longrightarrow$cross multiply to solve for x
$5x=28\times100$ $\longrightarrow$multiply
$5x=2800$ $\longrightarrow$ multiplication property of equality
$5x\div5=2800\div5$ $\longrightarrow$divide
$x=560$