Please solve this question immediately sir with the best explanation

Dear student,

Initally rate of decay of A is more since there are nmore nuclei of A. Uptil the rate of disintegratino of A is greater, the number of nuclei of B will keep on increasing and so the rate of disitegration of B would increase and that of A would decrease. After some time when the rates would become equal, the increase in nuclei of B would increase. Hence it is this time when B would have maximum nuclei.

Regards.