A company's direct labor standards for a given operation and the actual results for the current period are provided below:

Standard rates:

Advanced: $\backslash$$$18$ per hour

Trained: $\backslash$$$15$ per hour

Novice: $\backslash$$$10$ per hour

Time to produce one unit:

One $(1)$ Advanced worker at $30$ minutes each $=$

$30$ minutes per unit

Three $(3)$ Trained workers at $20$ minutes each $=$

$60$ minutes per

unit

Two $(2)$ Novice workers at $15$ minutes each $=$

$30$ minutes per unit

$120$ minutes per unit

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.