Let's denote crew A's work per week as A and crew B's work per week as B.
We are given that A = 58 ft per week and B = 59 ft per week.
We have to calculate how many weeks it will take both crews to complete the tunnel.
585 feet have already been dug from the south end. So, the total tunnel length that needs to be dug is 7605 - 585 = 7020.
Now, let's assume that both the crews continue to work at their respective rate of A = 58 ft/week and B = 59 ft/week.
Therefore, total tunnel length that needs to be dug in weeks = (7020 ft) / (A + B)
= (7020 ft) / (58 ft/week + 59 ft/week)
= 120.20 weeks
Hence, it will take a total of 120.20 weeks for both crews to complete the tunnel.