20 red marbles cost$3 while 40 marbels are available at$4.how much would it cost someone to buy 10 red marbles and 50 green marbles?

1.$3.50
2.$4.00
3.4.50
4.5.00
5.5.50

red

each is 3/20

green
each is 4/40 which is 1/10

so
10(3/20) + 50(1/10)

= 1.50 + 5.00

= 6.50
ah well, not on the list. Typo?