Xintai Taifeng Company wants to transport a batch of goods to a certain place, and intends to rent two kinds of trucks, A and B, from a car company. The information about renting these two trucks before is as follows. A-class trucks transport x tons at a time and B-class trucks transport y tons at a time.

Equations can be listed according to the meaning of the problem. 2x+3y= 15.5？ 5x+6y=35，

Solution: x = 4y = 2.5.

Namely: Class A trucks transport 4 tons at a time, and Class B trucks transport 2.5 tons at a time.

Freight payable: (4×4+6×2.5)×50= 1550 (RMB).

So the answer is: 1550.