corrections
1. Get the correct understanding of troposphere and the " 'pause ". Then...
2. Assume the equation of state holds good - then solve p = rho*R*T and appreciate where and why ISA is another concept entirely. Hint - the clue is in the equation, if and only if R is a constant then LHS must equal RHS and be the product of which two variables?
3. ?? Lost in translation but I fear something else is holding you back.
What meteorology text are you using and if under training by whom? If by chance you are responding to a multi-choice test then the examiner is often no better informed than the student!