(1)5吨=5000千克;
(2)6分米=60厘米;
(3)1吨+400千克=1400千克;
(4)1米-4分米=6分米;
(5)3千米=3000米;
(6)400米+600米=1千米;
故答案为:5000,60,1400,6,3000,1.