Last week, Ellen bought 4 apples for $2.40. This week she bought 9 apples for $5.40. If the cost per apple remains the same, how many apples could she buy next week?
A. 1 apple for $1.20
B. 6 apples for $3.40
C. 10 apples for $6.00
D. 13 apples for $8.20
The cost per apple is $2.40 / 4 = $<<2.40/4=0.60>>0.60 per apple.
Therefore, she could buy 6 apples for $0.60 x 6 = $3.60 next week.
Hence, the answer is B. 6 apples for $3.40. Answer: \boxed{B}.