Hi, I want to know why we divide 51300/54000 to get the std usage in the mix.ty

Coope and Sorcerer Co make product T42 in a continuous process, for which standard and actual
quantities in month 10 were as follows.
Standard Actual
Price price Std cost of
Quantity per kg Value Quantity per kg actual usage
kg $ $ kg $ $
Material P 40,000 2.50 100,000 34,000 2.50 85,000
Material Q 20,000 4.00 80,000 22,000 4.00 88,000
60,000 180,000 56,000 173,000
Losses occur at an even rate during the processing operation and are expected to be 10% of materials
input. So budgeted output for the month was 54,000 kg of T42 (= 60,000 kg × 90%). Actual output during
the month was 51,300 kg of T42.
Required
Calculate total usage, mix and yield variances.