Susanne will be x because both people use her as a comparsion. Bob's expression would be 4x, and Dakota's expression would be x - 3. If Dakota's and Bob's age sum is 93 then form the equation 4x + x - 3 = 93 to find Susanne's age. I'll do the steps below.
4x + x - 3 = 93
5x - 3 = 93
5x = 96
x = 19.2