To solve the problem, I make this table of three lines. The upper line counts weeks. Middle line shows the number of new members to join (the increment). The lowest line shows current total members. week 0 1 2 3 4 new members 1 2 3*2 = 6 9*2=18 27*2=54 to join Freda herself total current number of members 1 1+2=3 3+6=9 9+18=27 27+54=81 <<<---=== ANSWER