Help!!

I'm problably too late, but I am still answering,

Answer: B because by Jane ($10*3$) is 30 and then subtract the $20 and this is 10,

and by Chris is the same, but ($10*5$) is 50 and then subtract the $40 and this is also 10.

By A: Jane ($8*3$) is 24 and then subtract the $20 and this is 4,

and by Chris the same, but ($8*5$) is 40 and then subtract the $40 and this is 0 (difference: 4).

By C: Jane ($12*3$) is 36 and then subtract the $20 and this is 16,

and by Chris the same, but ($12*5$) is 60 and then subtract the $40 and this is 20 (difference: 40).

By D: Jane ($20*3$) is 60 and then subtract the $20 and this is 40,

and by Chris the same, but ($20*5$) is 100 and then subtract the $40 and this is 60 (difference: 60).

Straight