Nothing if you sell them back at $10,400 you will rather have to pay some fees for the trades. Ok, I know it is a typing mistake, so I'm just messing with you.
You can calculate your profit by the grown percentage of price. Let's say if the price is at $10k and you invest $100, and the price gets a little movement to reach $10,100 by tomorrow. It means the price has grown 1% since you invested, so your profit would be 1% of what you invested, which if you've invested $100 would be $1. All you need to do is to remember the starting price and then see the current price at the time of selling and then calculate the percentage of growth. Apply that percentage to your invested amount and you will come to know how much your investment have gained by now. It is actually quite complicated but you can do it if you know basic mathematics.
you'd equally have to factor in exchanger fees with most set at 0.5% thereby cutting the profit to 0.5%