We will take hours as units for time t and decays per hour (3600 Bq) as unit for decay constant for the solution below. (instead of per second).
Here, when we say an amount of substance, it means the number of Nuclei or atoms.
After t = 48 hours, the ratio of the amounts of the two radioactive substances is
The amounts of the two substance will become equal. That is both substances will have same number of (atoms or) Nuclei.