The exercise says: $$Both interarrival and activity times are exponentially distributed.$$ This simply means that the coefficient of variation of interarrival times and processing times is $1,$ that is$,$ CVi $=1$ and CVp $=1.$ In other words, the problem satisfies the as$-$ sumptions to use the performance.xls spreadsheet$$s $$infinite queue$$ tab to answer $8\mathrm{.}4($a$),$ and the $$finite queue$$ tab when analyzing parts $8\mathrm{.}4($b$),8\mathrm{.}4($c$),$ and $8\mathrm{.}4($d$).$

$$ The exercise says, $$For simplicity, assume that any number of incoming calls can be put on hold...$$ For part $8\mathrm{.}4($a$),$ assume that that there is a single CSR $($c $=1)$ and that there is a single waiting line that can be infinitely long $($K $=\backslash$infty $).$ For parts $8\mathrm{.}4($b$)$ and $8\mathrm{.}4($c$),$ there is still a single CSR $($c $=1).$