Hello there. To state the restrictions to the variables, remember that the quotient 1/0 doesn't exists, which means that any expressions on the denominator of a fraction can be equal to zero.
In this case, we have:
8/(x-2) = 4/(-9)
To find the restriction, note that the expressions on the denominator are a linear function and a constant, respectively.
This means that we want to find the restriction on the linear function, since the constant is not equal to zero on the right hand side.
x - 2 =\ 0 (=\ meaning not equal)
Sum 2 on both sides of the inequality
x =\ 2
This is the restriction for the variable x we wanted to find.