1) A(3, 9) = 9*8*7 = 504; A(2, 11) = 11*10 = 110;
A(3, 9) - A(2, 11) = 504 - 110 = 394.
A(2, 10) = 10*9 = 90; A(4, 12) = 12*11*10*9 = 132*90;
A(2, 10) - A(4, 12) = 90 - 132*90 = -131*90 = -11790
394 / (-11790) = -197/5895
2) C(3, 11) = 11*10*9/(1*2*3) = 11*5*3 = 165
C(4, 13) = 13*12*11*10/(1*2*3*4) = 13*11*5 = 715
165 - 715 = -550
C(2, 12) = 12*11/(1*2) = 6*11 = 66
C(3, 13) = 13*12*11/(1*2*3) = 13*2*11 = 286
C(2, 12) - C(3, 13) = 66 - 286 = -220
-550 / (-220) = 5/2 = 2,5