1)
when x is divided by 4 the remainder is 3;

when x is divided by 6 remainders are 1,5,3
so A INSUFF

2)
when x is divided by 3 the remainder is 5;

when x is divided by 6 remainders are 2,5
so B INSUFF

when
when x is divided by 4 the remainder is 3 and when x is divided by 3 the remainder is 5;

and when x is divided by 6 then remainder is always 5; will do
Both together SUFF

Ans C.