exp(-0.9/(1273*8.62*10^-5)

exp(-0.9/(1273*8.62*10^-5)

$$\small{\text{ $ e^{-\dfrac{0.9}{(1273\cdot 8.62 \cdot 10^{-5})}} = 0.0002741717276064 $}}$$

see: http://web2.0rechner.de/#exp(-0.9/(1273*8.62*10^-5) and push the "=" Button

and you get 0.0002741717276064