Which problem can be solved using the equation shown? 2 dollars and 50 cents x minus 2 dollars = 10 dollars and 50 cents

1) Will bought several books that cost $2.50 each and received a $2.00 discount on his total bill. If he paid $10.50, how many books did he buy?
2) Will bought several books that cost $2.00 each and received a $2.00 discount on his total bill. If he paid $10.50, how many books did he buy?
3) Will bought several books that cost $10.50 each and received a $2.00 discount on his total bill. If he paid $2.50, how many books did he buy?
4) Will bought several books that cost $10.50 each and received a $2.50 discount on his total bill. If he paid $2.50, how many books did he buy?