How much will a $7200 EE savings bond cost when you initially purchase it? Assuming the bond earns 3.09% annually, approximately how long will it take for the bond to reach its stated face value?

a. When you initially purchase it, the EE saving bond will cost $3600

b. Assuming the bond earns 3.09% annually, the length of time it will take for the bond to reach its stated face value is??

Need help with B please and thank you!