Final answer:
The direct materials quantity variance was calculated as unfavourable because more materials were used than the standard allowed, resulting in a c) $2,000 unfavourable variance.
Step-by-step explanation:
The direct materials quantity variance can be calculated by taking the difference between the standard quantity allowed for actual production and the actual quantity used, and then multiplying by the standard cost per unit of direct materials. Here, the standard quantity for 4,000 units would be 3 gallons per unit, amounting to 12,000 gallons (4,000 units × 3 gallons/unit). The actual quantity used was 12,500 gallons. The variance is therefore (12,000 gallons - 12,500 gallons) × $4 per gallon, resulting in a 500-gallon difference at $4 per gallon, which equals a $2,000 unfavourable variance since more materials were used than standard.