First let's calculate how much oil the cook uses per week.
15(2 kg) = 30 kg per 4 weeks
This means the cook averages 30 kg per 4 weeks →

or 7.5 kg per week
Next let's calculate how much oil the cook will need for 10 weeks.
7.5 kg/weeks × (10 weeks) = 75 kg ← the weeks units cancel out
Finally divide the amount of oil the cook needs for 10 weeks by the amount of oil in a 5 kg tin.
75 ÷ 5 = 15
ANSWER: The cook will need
fifteen 5 kg tins of oil.