Kyle and Ashley work at Sweet Treats after school. They sold a total of 144 boxes of lollipops. Kyle sold 60% as many boxes as Ashley. How many fewer boxes did Kyle sell than Ashley?

k = 0.60 a

k + a = 144
so
0.60 a +a = 144
1.60 a = 144
a = 144/1.60 = 90
then k = 144 - 90 = 54
90 - 54 = ????