Jake winters plans to invest $7,400 find the interest rate required for the fun to grow to $7,844 and 8 months

log(1 + rate) = {log(total) -log(Principal)} ÷ Years
total = 7.844   principal = 7,400  Years = .6666666

log(1 + rate) = {log(7,844) -log(7,400)} / .6666666
log(1 + rate) = {3.894537585 -3.8692317197} / .6666666
log(1 + rate) = 0.0253058653 / .6666666
log(1 + rate) = 0.0379588017

Now we  raise 10 to the power of 0.0379588017
10^0.0379588017 = 1.0913368046
which is 1 + the rate
rate = .0913368046 which equals
9.13368046 %

Source:
http://www.1728.org/compint2.htm