Your question is using the term "return" in an unusual way. Usually return refers to rate of return which in this case is the interest rate. For this problem, I will interpret return as the dollars earned as interest.
Also the formula you have for continuous compounding is not correct. A=P*e^(i*t) where A = Account value, P = initial balance, i = interest per year, and t = time in years. The symbol ^ means raised to the power of.
Let A(t) be the account value at time t in years.
Let r(t) = A(t)-3000
A(6) = $3000*1.07^6=$4502.19
r(t) = $1502.19
A(6) = $3000*(1+.07/12)^(6*12) = $4560.32
r(t) = $1560.32
A(6) = $3000*e^(.07*6) =$4565.88
r(t) = $1565.88