I need help with question C$!!!$

Exercise $13\mathrm{.}48$

The data below show the concentration of $N_2{O}_5$ vs$.$ time for the following reaction:

$N_2{O}_5(g)N{O}_3(g)+N{O}_2(g)$

a$)$ Determine the order of the reaction

Rate $=k[N_2{O}_5{]}^1$

:$.n=1$

b$)$ Determine the value of the rate constant

K$=6\mathrm{.}39$x$10^-3$ s$^-1$

C$)$ predict the concentration of N$2$O$5$ at $280$s