Consider two competing equipment $A$ and $B$. For a compound interest rate of $10\%$ per annum, in order for equipment $B$ to be the economically cheaper option, its minimum life (in years) is _____________ (rounded off to the next higher integer).
$\begin{array}{cc}\
&\text{$Equipment$} & \text{$Capital Cost$} & \text{$Yearly \: Operating$} & \text{$Equipment \: Life$}\\
&\text{} & \text{$(Rs)$} & \text{$Cost\:(Rs)$} & \text{$(Years)$} \\
&\text{A} & \text{80,000} & \text{20,000} & \text{4} \\
&\text{B} & \text{1,60,000} & \text{15,000} & \text{?} \\
\\ \end{array}$