The half life of Radium 214 is 2.46[s]. You can check half times at the following wikipedia article.
I am not sure what the 3 stands for, but I suspect that this is some sort of annotation/footnote that was not properly inserted in the webpage.
If you look at Text equation 1.29, the 492/620 is Temperature in Rankine.
$$T°F = T°R - 459.67$$
Ice point is 491.67°R. 160°F = 619.67°R.
If you do the math, it does not equal 0.0641, because the 369 is wrong. The math to get 0.0641 means 369 should be 359.
1 lb-mole of an ideal gas at 0°C and 1 atm occupies 359 $ft^3$ absolute.
The molecular weight of air ...