Per means for each, and it means divide: km/h is km ÷ h, and £/kg is £ ÷ kg.
So football pitches per squared squirrel is football pitches ÷ (squirrel × squirrel). The unit tells you what to do.
Every answer needs its unit: type the number, then pick the unit.
Each stage: a worked example, then 10 questions, easiest first.