Okay, to begin. Jessie is 24 years younger than her mother. So what we should first do is to subtract every possible age by 24 years. Which leaves us with 30, 6, and 4. Now if the sum of their ages is 84, we need to take all of the possibilities and add them to the other possibilities I've created.
30 + 54 = 84
6 + 30 = 36
4 + 28 = 32
Therefore, Jessie is 30 years old.