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?
During one minute the metro sells 5 tickets, so they earn 5 * 3 = $<<5*3=15>>15.
So in 6 minutes they would earn 15 * 6 = $<<15*6=90>>90.
#### 90