I just finished this paper

So basically try to think of all possible combinations that would give terms with

From the first part that you calculated
if you multiply this term with
)
possible terms with

would be

,

, &

The sum of their co-efficient = 48 given in the question
64a- (192X2) + 240=48
64a= 48-240+(192X2)
64a= 192
a=192/64
