please help with these i am so confused

The gas phase decomposition of dinitrogen pentoxide at 335K N2O5(g)2NO2(g)+1/2O2(g) is first order in N2O5. In one experiment, when the initial concentration of N2O5 was 0.0429M, the concentration of N2O5 dropped to 4.93103M after 343 seconds had passed. Based on these data, the rate constant for the reaction is s1. The rearrangement of cyclopropane to propene at 500C (CH2)3CH3CH=CH2 is first order in (CH2)3 with a rate constant of 6.70104s1. If the initial concentration of (CH2)3 is 0.231M, the concentration of (CH2)3 will be 0.0589M after s have passed