The molar mass of vitamin a (c20h30o).

Molar mass of C:  12.011 g/mol
The equation says C20, which means there are 20 carbon atoms in each molecule of Vitamin A.  So, we multiply 12.011 by 20 to get 240.22 g/mol carbon.

Molar mass of H:  1.0079 g/mol
The equation says C30, which means there are 30 hydrogen atoms in each molecule of Vitamin A. So, we multiply 1.0079 by 30 to get 30.237 g/mol hydrogen.

Molar mass of O: 15.999 g/mol
The equation says O without a number, which means there is only one oxygen atom in each molecule of Vitamin A.  So, we leave O at 15.999 g/mol.

Then, just add it up:
240.22 g/mol C + 30.237 g/mol H + 15.999 g/mol O = 286.456 g/mol C20H30O

So, the molar mass of Vitamin A, C20H30O, is approximately 286.5 g/mol.