You can't ever let this go negative. At least not at the grade you are in.
It can be 0.
So the domain must start at x = 7
sqrt(5*7 - 35) = sqrt(0) = 0
x can have any value (including 7) between 7 and infinity. If you choose a number less than 7 (like 6) the square root will go negative and that's not to be done.
