Yield variance

Sir, I m solving kit’s problems using your method. Mix is ok, but I have problems with yield variance. I calculate in columns: std mix (act.total usage) – std. cost-std mix(std. usage@act. production)- std. cost.
Problem from Kit: JC Ltd mixes three materials to produce a chemical SGR. Std cost card for producing 100 kg of SGR:
material A -50@$10/kg
material B-40@$5/kg
material C-20@$9/kg
During October 23180 kg of SGR were produced using following materials in kg:
material A – 13200
material B- 7600
material C- 5600

answer:7216 (A)

should I use method in kit or us it possible to solve using above- mentioned columns?