Calculate the relative formula mass (Mr) of BaCO3

So relative formula mass (M_r) just means the total mass of all the atoms within our molecule. So lets work out how many of each atom we have: Ba - 1, C - 1, O - 3Now we know the relative atomic mass of each of these (Ba - 137, C - 12, O - 3, as provided)
So now we multiply the masses by the amount of each atom and then sum the totals to give us the total mass of the molecule: ((137 x 1) + (12 x 1) + (16 x 3)) = 197