Question 32639
Let D,B, and M stand for the amount of money each has.
Then:
D+2=5B
M=D+B
B+D+M=80

Rearranging:
5B-D  =2
B+D-M=0
B+D+M=80

Solve using Cramer or row reduction.
I get Bob has $7, Darrell has $33, and Mary has $40
Cheers,
Stan H.