Answer:
Alex has twice as much money as Jennifer.
a = 2j
Jennifer has $6 less than Shannon.
j = s-6
j+6 = s
All together the three friends have $54.
a + j + s = 54
Replace a and s
2j + j + (j+6) = 54
4j = 54 - 6
4j = 48
j = 48/4
j = 12
Jennifer has $12
Alex= 2*12 = $24
Shannon = 24+12+s = 54
= 36+s = 54
s = 18
Shannon has $18