Answer
70.8
Work Step by Step
Since $R_{226} = R_{210}$,
$\lambda_{226} N_{226} = \lambda_{210} N_{210} $
$\frac{\lambda_{226} }{\lambda_{210} } = \frac{N_{210}}{N_{226}} $
$\frac{\lambda_{226} }{\lambda_{210} } = \frac{ln 2}{T_{1/2(226)}}. \frac{T_{1/2(210)}}{ln2}$
Cancel out ln 2, it becomes
$\frac{T_{1/2(226)}}{T_{1/2(210)}} = \frac{1600y}{22.6y} = 70.8$
