Answer:
1. Calculate Cookie Creations’ warranty liability for the shipping costs at December 31, 2020.
warranty liability = 30 x 10% x $60 = $180
2. Record the estimated warranty liability at December 31, 2020.
Dr Warranty expense 180
  Cr Warranty liability 180
3. Prepare the summary journal entry (or entries) to record the shipment of the six mixers (four from the 2020 sales and two from the 2021 sales) for warranty repair in 2021.
Dr Warranty liability (= $210 + $55) 265
  Cr Cash 265
4. Calculate Cookie Creations’ warranty liability at December 31, 2021.
warranty expense = ($210 - $180) + [(40 x 10% x $60) - $55] = $30 + $185 = $215
Dr Warranty expense 215
  Cr Warranty liability 215