Susan must choose a number between 61 and 107 that is a multiple of 4, 7, and 14.

84

7*12

14*6

21*4

The best thing to do is trial and error. You know multiples of 4 are going to be even numbers, so I now think of multiples of 7 that are also even numbers. 84 just happened to be the first number that the three aforementioned numbers divided into evenly. This method worked well for this problem because you had a small window to work within in 61-107.

The answere is 84

The method i used is long but it works

7, 14, 21, 28, 35, 42, 49, 56, 63, 70, 77, (84), 91, 98 105

4, * 10=40, 44, 48, 52, 56, 60, 64, 68, 72, 76, 80, (84), 88, 92, 96, 100, 104, 108

14, 28, 42, 56, 70, (84), 98