Rule of 72, Simple Interest, & Future Value

Solve the following problems.  Rule of 72, Simple Interest, & Future Value

Rule of 72

1. How many years does it take an investment to double earning 5%?  Rule of 72

2. How many years does it take an investment to double earning 8%?  Rule of 72

3. How many years does it take an investment to double earning 7.50%?  Rule of 72

4. How many years does it take an investment to double earning 9%?  Rule of 72

5. How many years does it take an investment to double earning 4%?  Rule of 72