What gases are no longer traceable about 19 km up why?

What is the answer for 734 divided by 6? Simplify i341 plus 3i89 minus 2i122 plus i5 minus 6i1008 plus i67 equals? What percent is 18 out of 600? What is the minimum length and width in meter of a box that can contain an object 56cm wide and 843 mm long? What is mean by TCID 50? How many hours is 9 am to 140 pm? Think of a number one through 10 then add 5 then add 3 then subtract the number that you thought of is you answer 8? What is 1m converted to feet and inches? What happened to the 2.3 trillion dollars spent by the Pentagon in 2001? How many times does 7 goes into 0? What is the ratio of 18 and 19? What was special about Mohenjodaro? What is 1.87 times 4.03? How do you write 521 billion? Is 432 only divisible by 2 3 or 2 and 3? What is the ball park estimate of 96-28 equals 68? In which categories do trapezoids belong? Is scissor a singular or plural noun? What objects would be about 5 cm long? What can you do at 12?