For the decomposition rate constant of methyl acetoxypropionate a value $0\mathrm{.}0317s^{-1}$ was found at $610K.$ The decomposition is carried out at this temperature in a closed vessel having a volume of $20d{m}^3.$ This reactor initially contained $0\mathrm{.}4$ moles of pure acetoxypropionate. Assuming ideal gas phase behaviour, calculate: a$)$ what will be the composition of the reaction mixture $($in mole$\%)$ after $90s$ from the start of the reaction, b$)$ reactor pressure at this time