You would set the equations equal to eachother and get x=-5/4 and then plug that in for x, i hope this helps!
The question is a bit ambiguous: you may mean

or

Anyway, in both cases, the domain of a function involving a square root is found by imposing the content of the root to be greateer than or equal to zero. So, in the first case you have

In the second case, you have
