First find the unit rate by dividing the price of 6 oranges by the amount of oranges in the bag. So $4.20÷6=0.7. 0.7 is the price of one orange. Since the dollar amount is small I just divided $4.20 by 2 and got $2.10 for three oranges. The question is asking how much he bought for $2.80 so add another .70 which is one more orange therefore he bought 4 oranges for $2.80