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?
answer: His girlfriend eats 6/2=<<6/2=3>>3 tomatoes per day
  So together they eat 6+3=<<6+3=9>>9 tomatoes a day
  That means they eat 9*7=<<9*7=63>>63 tomatoes a day
  So he needs 63/3=<<63/3=21>>21 tomato vines
  #### 21