Andrew is having 4 friends over who will get 3 donuts each, 4 x 3 = <<4*3=12>>12 donuts total.
Andrew’s mother wants to get 1 extra donut for each of Andrew’s friends, 3 donuts + 1 extra = <<3+1=4>>4 donuts for each of Andrew's friends.
Andrew’s mother is buying 12 + 4 extra donuts for Andrew’s friends = <<12+4=16>>16 total donuts.
Andrew’s mother is also going to get 3 + 1 extra donut for Andrew = <<3+1=4>>4 donuts.
Andrew’s mother will need to buy 16 donuts for Andrew’s friends + 4 donuts for Andrew = <<16+4=20>>20 total donuts.
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