First, add the 4 plants Mark gave away to the 20 he has left: 4 + 20 = <<4+20=24>>24
Then divide this number by 2 to find how many plants Mark had after two months: 24 / 2 = <<24/2=12>>12
Then divide that number by 2 to find how many plants Mark had after one month: 12 / 2 = <<6=6>>6
Finally, divide that number by 2 to find out how many plants Mark initially planted: 6 / 2 = <<6/2=3>>3
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