Try the questions in the PDF worksheet titled Molar Mass calculations. You can download a copy here.
Check your answers against the solution here.
Note an error in answer to 4c. The coefficient to oxygen should be 3/2.
Try the worksheet (Part 1 only), and check your answers from the Help tab.
The solution is available here.
Complete by (Sun) 21:00. This should take no more than 60 minutes.