Saint,
1. Make sure that you are keeping track of which side of the equation your numbers should be on. Also, check to make sure that your answer makes sense. If the diluted solution has a concentration of 0.393M HCl then how can the undiluted solution be less concentrated (0.0618 < 0.393).
2. First, look at the first part of the sentence. *Assuming the volumes are additive* What should be the first step to solving this problem? . Next, you have molar concentrations and volumes of several different compounds. You should attempt to figure out how much NO3- comes from each compound (You should be able to do this ) The easy part of this equation is that the NO3- is completely dissociative so you don't have to worry about how much free NO3- there is compared to bound. Once you have the amount from each compund you should be able to add them up and figure out the total concentration. Don't forget about the water!!!
Let me know if you need any more help
