Step 1 :The domain of a function is the set of all possible input values (often the "x" variable), which produce a valid output from a particular function. The domain of a function is the set of all possible x-values which will make the function "work", and will output real y-values.
Step 2 :For the function \(h(x)=f(x)-g(x)\), the domain is the set of all x-values that are in the domain of both \(f(x)\) and \(g(x)\).
Step 3 :The function \(f(x)=-\sqrt{x-3}\) is defined for all \(x \geq 3\), because the expression under the square root must be non-negative.
Step 4 :The function \(g(x)=x^{2}+3 x-8\) is a polynomial, and is defined for all real numbers.
Step 5 :Therefore, the domain of \(h(x)\) is the intersection of the domains of \(f(x)\) and \(g(x)\), which is \([3, \infty)\).
Step 6 :The correct form the domain can be written in is represented by reference number 1, and the correct value of \(a\) is represented by reference number 6.
Step 7 :Final Answer: \(\boxed{1, 6}\)