Answer
$e^{-3/2} \approx 0.22331$
Work Step by Step
The probability for $P(X \geq 12)$ can be computed as:
$P(X \geq 12) =\int_{12}^{\infty} \dfrac{1}{8}e^{-x/8} dx \\=\dfrac{1}{8} \lim\limits_{a \to \infty} \int_{12}^{a} e^{-x/8} dx \\=(-1) \lim\limits_{a \to \infty} (\dfrac{1}{e^{a/8}}-e^{-12/8})\\=e^{-3/2}\\ \approx 0.22331$
