Question: Steve decides to start eating more tomatoes and decides to grows his own cherry tomatoes.  He eats twice as much as his girlfriend.  He eats 6 per day.  If a vine can produce 3 tomatoes per week how many vines does he need?
Work out the solution step by step. 
Answer: 
His girlfriend eats 6/2=3 tomatoes per day
So together they eat 6+3=9 tomatoes a day
That means they eat 9*7=63 tomatoes a day
So he needs 63/3=21 tomato vines