139. Solving a chemistry problem

2. Prove that the reaction of the interaction of formic aldehyde and hydrogen peroxide with the formation of formic acid and water is a second-order reaction if after 2 hours after the start of the reaction it is completed by 50%, and after 2 hours 40 minutes the concentration of formic acid has become 0.285 mol / L. The initial concentrations of НСОН and Н2О2 are the same and equal to 0.50 mol / l.