Linear combinations of random variables — practice question

Large rice packets are placed into cartons, with 20 packets selected at random for each carton. The packet masses are normally distributed with mean $1010\,\text{g}$ and standard deviation $3.4\,\text{g}$. The masses of empty cartons are independently normally distributed with mean $50\,\text{g}$ and standard deviation $2.0\,\text{g}$. Small packets of rice are packed in boxes. The total masses of full boxes are normally distributed with mean $6730\,\text{g}$ and standard deviation $15.0\,\text{g}$. The masses of the boxes and cartons are distributed independently of one another.