Strontium ${?}_{38}^{90}Sr$ has a half$-$life of $29\mathrm{.}1$ yr $.$ It is chemically similar to calcium, enters the body through the food chain, and collects in the bones. Consequently, ${?}_{38}^{90}Sr$ is a particularly serious health hazard. How long $($in years$)$ will it take for $99\mathrm{.}9014\%$ of the ${?}_{38}^{90}Sr$ released in a nuclear reactor accident to disappear?

Number $$ Units