Any help and guidance would be appreciated! No idea how to work these :)

Okay so the combined gas law equations is PiVi/Ti = PfVf/Ti and you have to plug in what you’re given into the equation, cross multiple and then you have to isolate what you’re looking for. I had chemistry last semester and I’m not sure if I remember much, but I’ll attempt a question :)
I’m quite sure when you’re not given a value, you just consider it to be STP, but I’m not sure. I hope this just gives you an idea of what to do at least. Good luck!!!

Afraidsugar lol it’s the third one

Radon-222 or rn-222 has a half-life of 3.82 days. to determine the fraction of an original sample of rn-222 that remains unchanged after 7.646 days, we calculate the amount of rn-222 remaining after 7.646 days and divide it with the original amount. using 1 gram as a basis and using half-life calculation methods, we can determine that  0.249 or 0.25  grams of rn-222 will remain, and thus the fraction remaining is 0.25 or 1/4.