Question

Find the cost in cents of 1.7kg of potatoes at 70 #per kg

Answer 1

What is the unit of currency here?  "  #  " does not represent any currency, but rather is a representation of "pound" (the unit of weight, not the British pound).

If you do mean "British pound," then

70 British pounds
------------------------ = 41.2 pence (like pennies) per kg.
     1.7 kg