1) it must be fulfilled that the denominator is different from zero, then for this expression
x^2 -9 ⇒ x^2-3^2 = (x-3)(x+3)⇒ (x-3)(x+3) = 0 ⇒ x = 3 o x = -3 , the dominium is all numbers reals except 3 and -3
3(6)+8=26
I think 26 is the answer
16-A 18-B 19-D (not 100% sure on 16)
