Those small numbers below the element are the key. They tell you the mole ratio. So for Ag which has a 2 after it means that they are 2 "Ag"s.
Sulfur appears to have nothing. That isn't true. It has a 1, but as in math, the 1 is assumed to be there.
Every periodic table is different. So I can't give you exact numbers, but they will be close -- within +/- 1 of what your periodic table will show. So get out your periodic table and correct my numbers.
You periodic table should show that silver has a molar mass of 108. Remember, I'm rounding. You might show 107 point something large or 108 point something small. I will use 108
There are 2 of them
2 * 108 = 216
Sulfur is about 32 or so. There is one of them.
1 * 32 = 32
Now you add these two results together.
- 2Ag = 216
- 1 S = 32 Total: just add.
- Total 248 Answer to Ag2S
Now redo this with the numbers you got from your periodic table.
You can try these if you like
- CaCl2 = Answer 111
- CaS = Answer 72
- KBr = Answer 119