you can put x instead of ?. { this will be long process}
6(2/4) - 2(1/x) = 4(5/12)
12/4 - 2/x = 20/12 [ i divide 12/4 to get 3]
3 - 2/x = 5/3
-2/x = 5/3 - 3
-2/x = 5/3 - 3/1 [ i put 1 to make 3/1 ]
-2/x = (5/3) X 1 - (3/1) X 3 [ i took the LCM of 3 and 1 which is 3]
-2/x = 5-9/3
-2/x = -4/3 [ do the cross multiplication]
-2 X 3 = -4 X x
-6 = -4x
-6/-4 = x
3/2 = x
1.5 = x
hope this help you !!!!