Let N be the total number of $3 bags sold....then, 307 - N must be the number of $1 bags sold...so we have....price times units sold = revenue (total sales)
3(N) + 1(307-N) = 515 simplify
3N + 307 - N = 515
2N + 307 = 515 subtract 307 from both sides
2N = 208 divide by 2 on both sides
N = 104 and that's the number of $3 bags sold
So 307 - 104 = 203 = the number of $1 bags sold
