Let us assume the number of sandwiches made by Deli = x Amount of roast beef required for making 1 sandwich = (1/4) pound Total amount of beef that Marisa started with = 5 pounds Amount of beef that was left = (3/4) pounds Then [(1/4) * x] + (3/4) = 5 (x/4) + (3/4) = 5 (x + 3)/4 = 5 x + 3 = 5 * 4 x + 3 = 20 x = 20 - 3 = 17 So we can see from the above deduction that 17 Deli sandwiches was made by Marisa. I hope the procedure is clear enough for you to understand.