Question

If 2/3 inch on a map corresponds to an actual distance of 9 miles what distance on the map will represent 21 miles

Answer 1

2/3in=9mi
?in=21mi

we can set up a ratio and proportion, but I would fix that fractions because they tend to be messy

2/3in=9mi
multiply both sides by 3
2in=27mi

so now we have
2in:28mi=?in:21mi
$\frac{2in}{28mi}=\frac{?in}{21mi}$
multiply both sides by 21mi
the miles cancel and we get
$\frac{42in}{28}=?in$
1.5in=?in

1.5 inches represents 21 miles