A fisherman illegally drops some fish into a pond, and they quickly propagate (reproduce). The population growth of the new specifies is modeled by P(x) = 6b^x, where x is the time in weeks following the moment he dropped the fish into the pond and b is a positive unknown base. Find b if you know the lake contains 51 fish after 6 weeks.

a. 1.43

b. 8.5

c. 7.5

d. 1.23