Help! im on a timer What is the magnification formula?

StartFraction h Subscript I Baseline over h Subscript o Baseline EndFraction equals StartFraction d Subscript I Baseline over d Subscript o Baseline EndFraction.
The negative of StartFraction h Subscript I Baseline over h Subscript o Baseline EndFraction minus StartFraction d Subscript I Baseline over d Subscript o Baseline EndFraction. = 1
StartFraction h Subscript o Baseline over h Subscript i Baseline EndFraction equals the negative of StartFraction d Subscript I Baseline over d Subscript o Baseline EndFraction.
The negative of StartFraction h Subscript I Baseline over h Subscript o Baseline EndFraction equals StartFraction d Subscript o Baseline over d Subscript i Baseline EndFraction.