Material Cost Variance

A chemical is manufactured by combining two standard items of input A (standard price $60/kg.) And B (Standard price $45/kg.) in the ratio 60 % : 40%. 10% of input is lost during processing. If during a month 1,200 kg of the chemical is produced incurring a total cost of $69,600, what is the total material cost variance?

I’m not sure if I worked it out correctly.

Total Input: 0.90*x = 1200
x = 1200/0.90 = 1333.33 kg

Standard Total cost: (0.60*1333.33*$60) + (0.40*1333.33*45) = $72000

Actual Total cost incurred : $69600

Total material cost variance = $72000 – $69600 = $2400 Favourable

Sir, can you please correct if there are any mistakes.
Thanks.