First convert the bill amount to cents: $26 * 100 cents/dollar = <<26*100=2600>>2600 cents
Then multiply that amount by 5% to find the amount Gina normally tips: 2600 cents * 5% = <<2600*5*.01=130>>130 cents
Then multiply the bill amount by 20% to find the amount of a good tip: 2600 cents * 20% = <<2600*20*.01=520>>520 cents
Then subtract the good tip amount from the bad tip amount to find how much more Gina needs to tip: 520 cents - 130 cents = <<520-130=390>>390 cents
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