I’m pretty sure that the one you marked is correct
D, Because 7/15 + 9/15 is 16/15 + 4/15 =20/15 which equals 1 5/15 which turns into 1 1/3
A, 1/21 + 2/21 = 3/21 and that equals 1/7
C, 3/14+3/12 turns into 3/14+5/14= 10/14 - 8/14= 2/14=1/7
48 sets i believe since there are only 48 maximum of blue, green and yellow crayons therefore the 49th set would only contain a red crayons and a picture