Detail solution
Let's take the limit
$$\lim_{x \to \infty} \left(\frac{5 - x}{6 - x}\right)^{x + 2}$$
transform
$$\lim_{x \to \infty} \left(\frac{5 - x}{6 - x}\right)^{x + 2}$$
=
$$\lim_{x \to \infty} \left(\frac{\left(6 - x\right) - 1}{6 - x}\right)^{x + 2}$$
=
$$\lim_{x \to \infty} \left(- \frac{1}{6 - x} + \frac{6 - x}{6 - x}\right)^{x + 2}$$
=
$$\lim_{x \to \infty} \left(1 - \frac{1}{6 - x}\right)^{x + 2}$$
=
do replacement
$$u = \frac{6 - x}{-1}$$
then
$$\lim_{x \to \infty} \left(1 - \frac{1}{6 - x}\right)^{x + 2}$$ =
=
$$\lim_{u \to \infty} \left(1 + \frac{1}{u}\right)^{u + 8}$$
=
$$\lim_{u \to \infty}\left(\left(1 + \frac{1}{u}\right)^{8} \left(1 + \frac{1}{u}\right)^{u}\right)$$
=
$$\lim_{u \to \infty} \left(1 + \frac{1}{u}\right)^{8} \lim_{u \to \infty} \left(1 + \frac{1}{u}\right)^{u}$$
=
$$\lim_{u \to \infty} \left(1 + \frac{1}{u}\right)^{u}$$
=
$$\left(\left(\lim_{u \to \infty} \left(1 + \frac{1}{u}\right)^{u}\right)\right)$$
The limit
$$\lim_{u \to \infty} \left(1 + \frac{1}{u}\right)^{u}$$
is second remarkable limit, is equal to e ~ 2.718281828459045
then
$$\left(\left(\lim_{u \to \infty} \left(1 + \frac{1}{u}\right)^{u}\right)\right) = e$$
The final answer:
$$\lim_{x \to \infty} \left(\frac{5 - x}{6 - x}\right)^{x + 2} = e$$