Let f(x) = 3x ­- 6 and g(x) = x ­- 2. find f(g(5)) - ie. (f o g)(5) and its domain 1; all real numbers 3; all real numbers except x = 3 3; all real numbers except x = 2 3; all real numbers

Do this by finding g(5) first.  Replacing x with 5 in g(x) gives you that g(5) = 3.  Now replace that 3 in the x in f(x) to get that f(3) = 3.  As far as the domain goes,, they are both lines and the domain for lines is all real numbers.

She should use 12/3 to measure