$(12$ points$)$ Determine the half$-$life $($in each case$)$ of this signal with starting voltages of $6$ V$,4$ V$,$ and $2$ V $($i$.$e$.,$ determine the amount of time it takes for the signal to go from $6$ V $->3$ V$,4$ V $->2$ V$,$ and $2$ V $-1$ V$).$

$(8$ points$)$ Based on your results for part b$,$ what is your conclusion about the assertion that this voltage signal is exponential? Explain your reasoning.