Question

How do you solve `1/2 x = 40`?

Answer 1

Consider that you can move `1/2` to the right of your expression (but inverting it) as:
`x=(2/1)40`
So that `x=40*2=80`
Remember that your equation is like a balance; everything you move from one side to the other (of the equal sign) must change sign. In this case on the left you had a division by `2`...it goes to the right as a multiplication by `2`.
:-)