The formula to determine the materials to be purchased is

$($units to produce times materials required for each unit$)$ plus

desired ending materials inventory minus beginning materials.

inventory

$($units to produce divided by materials required for each unit$)$

minus desired ending materials inventory plus beginning ma$-$

terials inventory

$($units to produce divided by materials required for each unit$)$

plus desired ending materials inventory minus beginning ma$-$

terials inventory

$($units to produce times materials required for each unit$)$ minus

desired ending materials inventory plus beginning materials

inventory