Brenda’s mice had 3 * 8 = <<3*8=24>>24 baby mice.
She gave Robbie 24 / 6 = <<24/6=4>>4 mice.
Thus, she sold 3 * 4 = <<3*4=12>>12 mice to the pet store.
She had 24 - 12 - 4 = <<24-12-4=8>>8 mice remaining.
She sold 8 / 2 = <<8/2=4>>4 as feeder mice.
Thus, Brenda had 8 - 4 = <<8-4=4>>4 mice left.
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