you have 30.0 grams of a chemical element. After a certian amount of time, you have 3.75 grams remaining. How many half lives have you gone through?ASAP PLEASE

Nitrogen dioxide decomposes according to the reaction 2 no2(g) ⇌ 2 no(g) + o2(g) where kp = 4.48 × 10−13 at a certain temperature. if 0.70 atm of no2 is added to a container and allowed to come to equilibrium, what are the equilibrium partial pressures of no(g) and o2(g)