$PV($ asset $)=PV($ revenue $)-PV($ fixed $)-PV($ variable $)$

$PV($ revenue $)=PV($ fixed $)+PV($ variable $)+PV($ asset $)$

${}_{\text{r}\text{e}\text{v}\text{e}\text{n}\text{u}\text{e}}={}_{\text{f}\text{i}\text{x}\text{e}\text{d}}\frac{PV(\text{f}\text{i}\text{x}\text{e}\text{d})}{PV(\text{r}\text{e}\text{v}\text{e}\text{n}\text{u}\text{e})}+{}_{\text{v}\text{a}\text{r}\text{i}\text{a}\text{b}\text{l}\text{e}}\frac{PV(\text{v}\text{a}\text{r}\text{i}\text{a}\text{b}\text{l}\text{e})}{PV(\text{r}\text{e}\text{v}\text{e}\text{n}\text{u}\text{e})}+{}_{\text{a}\text{s}\text{s}\text{e}\text{t}}\frac{PV(\text{a}\text{s}\text{s}\text{e}\text{t})}{PV(\text{r}\text{e}\text{v}\text{e}\text{n}\text{u}\text{e})}$

WHY????Can you show the detailed process???