It's true because since Dallas, Texas is in the United States it is snowing in the United States. Even though all of the United States isn't snowing, Texas is still apart of the United States. Therefore, the following is true.
Because he starts off with 10 dollars, and x is the amount he spends on an item, y is showing the change that he would get from paying with a 10 dollar bill, so it's what's left over from that 10 dollars.
