i need help solving, ty:)

Ethyl chloride, CH3CH2Cl, used to produce tetraethyllead gasoline additive, decomposes when heated, to give ethylene and hydrogen chloride. CH3CH2Cl(g)C2H4(g)+HCl(g) The reaction is first order. In an experiment, the initial concentration was 0.00100M. After heating at 500C for 155 seconds, the concentration of ethyl chloride was reduced to 0.00083M. What is the concentration of ethyl chloride consumed after a total of 400 seconds