Question 16693
First of all you're interpreting the problem wrong.  g(-1) doesn't mean g * -1.  g is a function so it depends on certain parameter x.  We know g(x) = {{{x^2 - 3x}}} so to find g (-1) you simply put the value of x = -1 into the equation.
{{{(-1)^2 - 3(-1)}}} = 1 + 3 = 4.
Now you need to find {{{sqrt(g(-1))}}}} which is simply {{{sqrt(4)}}} = 2.

Hope this helps.