conversations.from: human
conversations.value: Dorothy, Julia, and Robert go to the store to buy school supplies. Dorothy buys half as many pens as Julia. Julia buys three times as many pens as Robert. Robert buys 4 pens. If one pen costs $1.50, how much money did the three friends spend in total on pens?
  Give me a detailed solution.
conversations.from: assistant
conversations.value: Julia buys 4 * 3 = 12 pens
  Dorothy buys 12/2 = 6 pens
  The total number of pens purchased is 4 + 12 + 6 = 22 pens
  The total cost of the pens is 22 * $1.50 = $33