PLEASE HELP༼ つ ◕◡◕ ༽つ How does this evidence proves that the law of conservation of mass is presented in the mixing of baking soda and vinegar in a closed system?

For the reaction c6h14(g) & longrightarrow; c6h6(g) + 4h2(g), δp(h2)/δt was found to be 2.5 x 10-2 atm/s, where δp(h2) is the change in pressure of hydrogen. determine δp(c6h14)/δt for this reaction at the same time.