Assalamu'alaikum Qaza? do you mean qashar? Qashar is shortening 4 raka'ah salah into 2 raka'ah. It's only for salah Zuhur, ashar, and isha. Subh and maghrib cannot be shortened. And this is only for Muslim who is in traveling (musafir) While combine two salah in one time is Jama. Salah which can be combined are zuhur and ashar, also maghrib and isha. Subuh cannot be combined. I cannot say combine ashar and maghrib is impermissible, but there is no base to combine ashar and maghrib. If you miss zuhur, you can do zuhur in ashar time. Do 4 raka'ah zuhur, then 4 raka'ah ashar. Under certain circumstance, jama can be combined with qashar.