[填空题]
A typical banana contai6;(ufjr+yuix4: zlbjh(wng /vf 4wrfp; 6*dx ns 400 mg of popk u; 86m,eajstassium, of which a small fraction is the radio,a;mus e8k6jpactive isotope $_{19}^{40}\text{K}$ (see Appendix B). Estimate the activity of an average banana due to $_{19}^{40}\text{K}$. $\lambda N$ = $\ \text{decays/s}$
