$a) \displaystyle\lim_{x \to 2} (3f(x)-2x^2)\\ =\displaystyle\lim_{x \to 2} 3f(x)-\displaystyle\lim_{x \to 2} 2x^2\\ =3\displaystyle\lim_{x \to 2} f(x)-2\displaystyle\lim_{x \to 2} x^2\\ =3.(-2)-2.2^2\\ =-14\\ b)\displaystyle\lim_{x \to -\infty} \dfrac{3x^2-x+10}{ax^2-x-11}\\ =\displaystyle\lim_{x \to -\infty} \dfrac{3-\dfrac{1}{x}+\dfrac{10}{x}}{a-\dfrac{1}{x}-\dfrac{11}{x}}\\ =\displaystyle\lim_{x \to -\infty} \dfrac{3-\dfrac{1}{x}+\dfrac{10}{x}}{a-\dfrac{1}{x}-\dfrac{11}{x}}\\ =\dfrac{3}{a}\\ =\dfrac{2}{3}\\ \Rightarrow a=\dfrac{9}{2}\\ \Rightarrow a-a^2=\dfrac{-63}{4}$
