Penicillin N is an antibacterial agent that contains 8.92% of sulphur by mass. What is the molar mass of penicillin N?

One atom of sulphur is present per one molecule of Penicilin N.

Now since, 8.92 gm of sulphur is present in 100 gm of penicillin N.

Therefore, 32 gm sulphur will be present in = $\frac{100\times 32}{8.92}$= 358.74 grams of Penicilin N. 
Hence molar mass of Penicilin N is 359 grams (approx.)