how many formula units are in 5.1g of TiOs?

how many moles of barium nitrate contains 6.80x10 to the 24th formula units

By formula units I assume you mean molecules.

Answer these questions, and you should see how to get the answer:
What is the molecular weight of TiOs?
How much does one mole of TiOs weigh?
How many molecules are in this mass of TiOs?
Therefore, How many molecules are in 5.1g of TiOs?

The second question is very clever, and is there to make you think about the definition of the mole:
How many molecules are in one mole of Barium Nitrate?
How many moles contain 6.8x10^24 molecules?
Note: The above is true for any compound or element, not just Barium Nitrate.

If you need further help, just ask :)