Remember that the molar mass of each element given in the question you can find it in the periodic table.
The molar mass of Al is 27 g/mol, the molar mass of S is 32g/mol, and the molar mass of O is 16 g/mol.
We have to do an algebraic sum to find its molar mass. You can see that we have 2 moles of Al, 3 moles of S and (3)(3) = 9 moles of oxygen. The algebraic sum would be the molar mass of each element mmultiplied byits molar mass and then sum all the results we obtained, like this:
27g/mol×2+16g/mol×9+32 g/mol×3=294 g/mol.
The answer would be that we have 294 g/mol of Al2(SO3)3.