The tables show the cost of different numbers of t-shirts ordered at two different stores, store p and store q:

store p

number
of t-shirts cost (in $)
3 $18
6 $36
9 $54

store q

number
of t-shirts cost (in $)
2 $10
4 $20
8 $40

which of these explains which store has a better buy?
store q, because the ratio of the number to the cost is 1: 6 in store p and 1: 5 in store q
store q, because the ratio of the number to the cost is 6: 1 in store p and 5: 1 in store q
store p, because the ratio of the number to the cost is 3: 21 in store p and 2: 12 in store q
store p, because the ratio of the number to the cost is 21: 3 in store p and 12: 2 in store q