Chemical Engineering Reaction

Compute the residence time required for Feed A in a CSTR 1-reactor tank to achieve a fractional conversion of 80%. The reaction taking place is a 2-order reaction 2A=R+S whose constant temperature rate is shown by the rate equation r=2.5CA2, initial feed concentration is given as CA,O=4Kmolm3. What is the ratio of reactor volume to volumetric flow rate for conversion to be 80%