JEE Mains 1-Feb-2023 Shift 1 Solved Paper

A and B are two substances undergoing radioactive decay in a container. The half life of A is 15‌min and that of B is 5‌min. If the initial concentration of B is 4 times that of A and they both start decaying at the same time, how much time will it take for the concentration of both of them to be same? ________ min.