and again the question doesn't seem to be properly framed.

A and B have only 10 dollars for their selections. Is the money enough for both of their selections?

1). B costs 4 dollars more than A

B = 4 + A
If A = 1, B = 5, then 10 dollars will be sufficient for their selections
If A = 100, B = 104, then 10 dollars will not be sufficient for their selections

2). B costs twice as much as A

B = 2A
If A = 1, B = 2, then 10 dollars will be sufficient for their selections
If A = 100, B = 200, then 10 dollars will not be sufficient for their selections

From 1 and 2

B = 4 + A
B = 2A
2A = 4 + A
A = 4 and B = 8, then 10 dollars will not be sufficient for their selections
IMO C