Take the given weight (784.616g) and divide it by the atomic weight of H2SO4.
The atomic mass can be found under the element symbol on the periodic table. You must add the atomic mass for each element in H2SO4 to get the total. The total atomic mass for H2SO4 will be about 98g.
Then divide the weight by this number.
784.616g/98g = 8.006 moles
Therefore, there is approximately 8 moles.