if she collects 1 on the first day, and she collects 3 times that on the second day, she collects 1x3=3 shells the second day. The third day, she collects 3 times that amount, so 3x3=9 shells. The fourth day, she collects 3 times that amount, 3x9=27, and the fifth day, 27x3=81 shells