A transponder receives the same number of orders each day. Currently, he has some pending orders (back logs) to be shipped. If he uses 7 trucks, then at the end of the 4th day, he can clear all the orders. Alternatively if he uses only3 trucks, then all the orders are cleared at the end of the 10th day. What is the minimum number of trucks required so that there will be no pending orders at the end of the 5th day?