One ticket to the underground costs $3. In one minute, the metro sells an average of 5 such tickets. What will be the earnings from the tickets in 6 minutes? Let's think first. Chain of thought:
During one minute the metro sells 5 tickets, so they earn 5 * 3 = $15. So in 6 minutes they would earn 15 * 6 = $90.
Therefore, the answer is 90.