Answer :
answer 3Sn+ 4H3pO4= 6H2+Sn(PO)4
1 Sn 3 Sn
3 H 2 H
1 P 4 P
4 O 16 O
then you have to make the numbers the same for each side
so you get by putting the 3 infront of Sn 4 infront of the H3PO4 and 6 infront of the H2
3 Sn 3 Sn
12 H 12 H
4 P 4 P
16 O 16 O
1 Sn 3 Sn
3 H 2 H
1 P 4 P
4 O 16 O
then you have to make the numbers the same for each side
so you get by putting the 3 infront of Sn 4 infront of the H3PO4 and 6 infront of the H2
3 Sn 3 Sn
12 H 12 H
4 P 4 P
16 O 16 O