Each day, mama bird needs to catch 6 x 3 = <<6*3=18>>18 worms.
For 3 days, she needs 18 x 3 = <<18*3=54>>54 worms.
She already has 13 - 2 = <<13-2=11>>11 worms.
With papa bird’s catch, they have 11 + 9 = <<11+9=20>>20 worms.
To feed the babies for 3 days, she needs to catch 54 - 20 = <<54-20=34>>34 more worms.
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