11: To add 3/8 and 2/5 you need to find the least common denominator (in this case 40), and change both fractions by multiplying to get the least common denominator and add them together
2/8 = 10/40
2/5 = 16/40
16/40 + 10/40 = 26/40 = 13/20
12 a: 5/6 = 45/54
4/9 = 24/54
45/54 - 24/54 =21/54
b: 7/10 = 56/80
3/8 = 30/80
56/80 = 30/80 = 26/80 = 13/40
