Answer
$$9.0 \times 10^{8} \mathrm{Bq}
$$
Work Step by Step
Using Eq. $42-16$ with Eq. $42-18$, we find the initial activity:
$$
R_{0}=R e^{t\ ln 2\ / T_{1/2}}=\left|7.4 \times 10^{8} \mathrm{Bq}\right| e^{24 \ln 283.61}=9.0 \times 10^{8} \mathrm{Bq}
$$
