a) Girl Guides selling biscuits made $2 profit for every 6 packets of biscuits they sold.
    How many packets of biscuits would they need to sell to make $500 profit?

b) If they made $2.50 profit for every 8 packets of biscuits they sold,
    how many packets would they now need to sell to make $500 profit?

c) If every 8 packets made them $2.50 profit, and on average they sold 2 packets per house they visited,
    how many houses would they need to visit to make the $500 profit?