You can expose the length and diameter from the reactor using a virtual information port. You can expose the volumetric or mass flow rate from the feed stream from a measure unit. You can then calculate the residence time from an information calculator.
for someone with same question, here is the solution and the link to the pdf where the problem was obtained. the answer, t, is in seconds converted to minutes one gets 10.2 minutes same as aspen's. https://lms.nchu.edu.tw/mobile/media/41080