May I ask for an explanation and solution to the question for a better understanding. Thank you! 4. Pierce Corporation has the following gross profits for 2018 and 2019: Sales = XXXXXXXXXXP810,000;...

May I ask for an explanation and solution to the question for a better understanding. Thank you!

4. Pierce Corporation has the following gross profits for 2018 and 2019: Sales = 2019 - P810,000; 2018 - P792,000. Cost of sales = 2019 - 480,000; 2018 - 464,000. Gross profit = 2019 - P330,000; 2018 - P328,000. Sales price was 10% lower during 2019. The sales volume variance must be: