Molar mass can be determined by adding the atomic masses of each individual element, depending on how many times they appear. You can find how many times they appear by looking at their respective subscripts. Atomic masses of each element can be found on the periodic table.
For example, in #1
Multiply the mass of Lithium (6.941) by 4, because there are 4 lithium molecules.
Multiple the mass of Phosphorus (30.974) by 2 because there are 2 Phosphorus molecules.
And multiply the mass of oxygen (15.999) by 7 because there are 7 oxygen molecules.
After you have those values, add them together to find the total molar mass of the compound.
