With the boy’s contribution, there are 12 + 6 = <<12+6=18>>18 walnuts.
When he drops 1, now they have 18 - 1 = <<18-1=17>>17 walnuts.
The girl adds to their stash, making the count 17 + 5 = <<17+5=22>>22 walnuts.
When the girl eats 2, the final count is 22 - 2 = <<22-2=20>>20 walnuts.
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