First find how much weight the labrador puppy gains: 40 pounds * 25% = <<40*25*.01=10>>10 pounds
Then add that weight gain to the puppy's starting weight: 40 pounds + 10 pounds = <<40+10=50>>50 pounds
Then find how much weight the dachshund puppy gains: 12 pounds * 25% = <<12*25*.01=3>>3 pounds
Then add that weight gain to the puppy's starting weight: 12 pounds + 3 pounds = <<12+3=15>>15 pounds
Then subtract the dachshund puppy's weight from the labrador puppy's weight to find the difference: 50 pounds - 15 pounds = <<50-15=35>>35 pounds
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