Using the rule of $72,$ approximate the following amounts. Look up Rule of $72$ online.

a$.$ If the value of land in an area is increasing $7$ percent a year, how long will it take for property values to double?

b$.$ If you earn $10$ percent on your investments, how long will it take for your money to double?

c$.$ At an annual interest rate of $5$ percent, how long will it take for your savings to double?