a)

25 div 3 = 24:3=8

73 div 7 = 70:7= 10

31 div 7 =  28:7= 4

25 mod 3= 25-24=1

73 mod 7 = 73-70=3

31  mod 7 = 31-28=3

b)

2 div 3 + 1 = 0+1=1

17 - 23 div 7 = 17 - 3 = 14

31 div (7+5) = 31 div 12 = 2

25 mod 3 + 25 div 3 = 8+1=9

47 div (3 mod 7) = 47 div 3 = 15

31 mod (7 div 2) = 31 mod 3 = 1