A patient is prescribed 173 mg of medication. The medication comes in the form of a solution, 87 mg/4 mL. To the nearest millilitre, how many millilitres does the patient receive in one dose? Include the unit mL.

87 mg needs 4 mL

1 mg needs 4/87 mL
173 mg needs (4/87)(173) mL or appr 7.954 mL

or

just use a ratio:
87/4 = 173/x
87x = 4(173)
x = 4(173)/87 ----> same as above