if we apply the usual MR=MC rule for domestic markets, we see that 5-3q = q and p>3 so the monopolist can sell cheaper overseas anyway. this is a case for dumping.
So, i equate foreign price with MC to get maximum quantity produced. I have total q now. However, we know that monopolist will charge some other price in the domestic market.
Thus to find domestic production, equate MR = Foreign price and find domestic q. calculate domestic p through the demand function.
The difference between total production and domestic production would be your exports.
“Operator! Give me the number for 911!”