Iam doing my math homework and i don't know how to do these type of problems -21=y/2

To solve these problems, you have to isolate the variable. the easiest way to think about this is that if you have to do an operation on the opposite side of the equal sign, do the opposite. for example, you'd divide y by 2, so to solve the problem you multiply 2 by -21. this leaves the answer = y. hope this helps.