Answer
Proportion states that two ratios or fractions are equal.
As per the statement:
A scale on a hiking map shows that 1.5 inches represents 4 miles.
⇒On hiking maps: 1.5 inches = 4 miles
We have to find actual miles are represented by 6 inches on the map
Let x be the actual miles.
by definition of proportion we have;

By cross multiply we have;

Divide both sides by 1.5 we have;
miles
therefore, 16 actual miles are represented by 6 inches on the map