In a radioactive decay process, the activity is defined as $A=-\frac{dN}{dt},$ where 𝑁(𝑡) is the  number of  radioactive nuclei at time 𝑡. Two radioactive sources, S1 and 𝑆2 have half  lives in the ratio 3:5. At t =0, they have the same number of nuclei. Activities of  𝑆1and 𝑆2are 𝐴1and 𝐴2, respectively at a time which is equal to 3 half-lives of S2. The  ratio 𝐴2/𝐴1is X then, 2.5X is equal to ____________