John has a collection of sneakers. He decides to buy 3 more pairs of sneakers each month for 4 months. If he already has 6 pairs of sneakers, how many pairs of sneakers will he have in total after 4 months?
John buys 3 pairs of sneakers per month for 4 months, totaling 3 * 4 = <<3*4=12>>12 pairs of sneakers.
Adding this to the 6 pairs he already has gives him 12 + 6 = <<12+6=18>>18 pairs of sneakers. Answer: \boxed{18}.