I got it!i need to use the fact that if np is the number of Sylow-p subgroup of group G then np divides the index if P in G,(where Pis the Sylow-p subgroup of G)..

So if P1 is the Sylow-2 subgroup of A4 then np is either 1 or 3,where cardinality of P1 is 4..so there is only one Sylow-2 subgroup of A4 as there are only three elements in A4 of order 2..(so these three elements along with identity form the only Sylow-2 subgroup of A4)..

Similarly for Sylow-3 subgroup of A4..The possibilty of np is 1or 2 or 4..nand then as above..

Correct??