To solve for the mass of H2SO4, we need to first find the molar mass of H2SO4.

H2SO4:

2 Hydrogen atoms $H$ = 2 g/mol 1 Sulfur atom $S$ = 32 g/mol 4 Oxygen atoms $O$ = 4 x 16 g/mol = 64 g/mol

Adding these values together, we get:
2 + 32 + 64 = 98 g/mol

Now, we can use the given mass of SO3 to find the mass of H2SO4.

Moles of SO3 = Mass / Molar Mass
Moles of SO3 = 240g / 80g/mol = 3 moles

Since SO3 and H2SO4 have a 1:1 mole ratio, the moles of H2SO4 is also 3 moles.

Mass of H2SO4 = Moles x Molar Mass
Mass of H2SO4 = 3 moles x 98 g/mol = 294g

Therefore, the mass of H2SO4 is 294 grams.