Explain how to solve 643 = 4x160 + n

First you will have to multiply 4 and 160 which will be 640

then write 640 in the place of 4x160 so you should have 643=640+n

you then will subtract 640 with 640 and they should console out

then subtract 643 with 640 you should get 3

so your answer should be 3=n

Omg really? Im in Middle School and i never saw anythin like this in Elementary School?