A = 6/7 -4/7 x 5/2
A = 6/7 - 20/14
A = 12/14 -20/14 = 8/14 = 4/7
B = 3/4 -4 : 3/4 +1/3
B = 3/4 - 16/4 : 9/12 + 4/12
B = -13/4 : 13/12
B = -13/4 x 12/13
B = -156/52 = -78/26 = - 39/13 = -3
C = 3² x 2 - 125 x 10^6
C = 18 - 12.5 = 5.5
D = 3.2 x 5 x 10^-5 x 10^6 : 4 x 10^-2
D = 16 x 10 : 4 x 10^-2
D = 4 x 10^3
