chemist ??? (i see on internet but not this chemistry lesson)

X is the HCl solution of concentration x mol / l. Y is Na2CO3 solution of concentration y mol / l. Slowly drip 100 ml X into 100 ml Y, after the reaction obtained V1 liters of CO2 (standard standard). Slowly drip 100 ml Y into 100 ml X, after the reaction obtained V2 liters of CO2 (standard standard). Know the ratio V1: V2 = 4: 7. Ratio x: y equal; WHATER HACK, CHEMIST