The answer would be 3/12 was used on the recipe. If 3/12 was used on the recipe and we know 2/12 was used to make a sandwich, 3/12 + 2/12 =5/12 used and that holds true being as there is 7/12 of the loaf left. 12/12 - 5/12 = 7/12
Hope I helped. Please mark me brainliest! :)