设(2)班捐款为x元,(3)班,(4)班捐款为y元,根据题意,列方程组得 x?y=300 x+2y+2000=10400 ,解得: x=3000 y=2700 .答:(2)班的捐款金额为3000元,(3)班,(4)班的捐款金额为2700元.