It would be cheaper to buy them for $4.25. The pattern is 1 orange costs $0.45 because 1.35/3 = 0.45, 1.80/4 = 0.45, and 2.25/5= 0.45. So if this pattern continues we can find how much 10 oranges would cost by 10*0.45= 4.50, so it would cost $4.50. Since $4.50 is more than $4.25, then we know the bag for $4.25 would cost less.
hope that helped! :)
