Given :
A 18-mile taxi ride takes 21 minutes and costs $12.60.
To Find :
The cost of a 39- mile taxi ride. What unit price do you need.
Solution :
Unit price per mile :
[tex]p=\dfrac{12.60}{18}\\\\p = \$0.7\ /mile[/tex]
Cost of 39 mile taxi ride :
[tex]C = 39\times p\\\\C=39\times 0.7\\\\C=\$27.3[/tex]
Therefore, unit price is $27.3 and unit price is $0.7 / mile .
Hence, this is the required solution.