cant a and b be swithed as 48
number of permutations of whole;120
number of permutations with a and b together:24
number f permutations with c and d together: 24
number of where tey are both together(ab and cd): 12
24+24-12=36
120-36=84
isn't a and b together 48 because you can switch them.
oops forgot about that
48+48=96-12=84
36 permutation
+539 
