can someone explain the steps in solving these?

The mixing ratio of PAN (C2H3NOs) was 2.4 ppm at 32 km height. The temperature was - 36 C and the corresponding pressure 1.2 x 103 Pa. The rate coefficient of PAN thermal decomposition can be described by an Arrhenius equation with a pre-exponential factor A= 1.58 x1016 and an activation energy Ea = 112.5 kJ/mol. a) Give the PAN concentration in molecules cm3. (Your calculations should be transparent and easy to follow). b) Write the decomposition reaction of PAN. c) What is the natural lifetime of PAN at given altitude? R= 8.314 ) mol-1 K-1 and Avogadros number Na = 6.02 x 1023 molecules mol-1