A Company's Direct Labor Standards for a Given Operation and the Actual

A company's direct labor standards for a given operation and the actual results for the current period are provided below:
Standard rates:
Advanced: $18 per hour
Trained: $15 per hour
Novice: $10 per hour
$\begin{array}{|l|r|}\hline \text { Time to produce one unit: } \\\begin{array}{l|r}\hline\text { One (1) Advanced worker at } 30 \text { minutes each }= & 30 \text { minutes/unit } \\\hline \text { Three (3) Trained workers at } 20 \text { minutes each }= & 60 \text { minutes/unit } \\\hline \text { Two (2) Novice workers at } 15 \text { minutes each }= & 30 \text { minutes/unit } \\\hline & 120 \text { minutes/unit }\\\hline\end{array}\end{array}$

Actual Results:
Units produced: 4,000
Labor used:
2,200 hours of Advanced workers
4,300 hours of Trained workers
1,900 hours of Novice workers
Required:
(Be sure to indicate whether the variance is favorable or unfavorable.)
a. Compute the labor efficiency variances for each worker level.
b. Compute the labor mix variances for each worker level.
c. Compute the labor yield variances for each worker level.