$7\mathrm{.}32$ An exponential voltage decay v$($r$)=$ u$(0)$e $1$t$/$ si ob$-$ served with na oscilloscope. If it is found that u$(1$ us$)=12\mathrm{.}28$ Vand u$(7$ us$)=3\mathrm{.}7$ V$,($a$)$ find u$(0)$ and t$,$ and $($b$)$ pre$-$ dict v$10$ ps$).$