C89 Lin Wan'er's Birthday

As Qin Feng spoke, he started writing out the steps to solve the problem on the blackboard.

The teacher saw Qin Feng writing the solution to the problem. The students in the class couldn't understand it, but he could understand it. He didn't expect Qin Feng to have already started studying mathematics in university.

"Stop, stop, stop. You don't need to write anymore, Qin Feng. You can leave now