Perform the various calculations with your collected data as

Perform the various calculations with your collected data as listed in the lab

Solution

Pb(NO3)4+K2CrO4-> Pb(CrO4)2+KNO3

you have 4 NO3 on the left, so you need to have 4 NO3 on the right. How? Add a 4 in front of KNO3.

Pb(NO3)4+K2CrO4-> Pb(CrO4)2+4 KNO3

Now you have 4 K on the right, but only 2 K on the left. So add a 2 in front of K2CrO4.

Pb(NO3)4 + 2 K2CrO4-> Pb(CrO4)2 + 4 KNO3

Now, you have one Pb on the left, one Pb on the right
4 NO3 on the left, 4 NO3 on the right
4 K on the left, 4 K on the right
2 CrO4 on the left, 2 CrO4 on the right