Answer
6 additional hours
Work Step by Step
Because the cost increases by \$5 for each additional hour, spending an additional \$30 will provide 6 ($\$30\div6$) additional hours.
$Slope=\frac{\Delta y}{\Delta x}$
$5=\frac{30}{\Delta x}$
$5\div5\times\Delta x=\frac{30}{\Delta x}\div5\times\Delta x$
$\Delta x=6$
