The per-unit standards for direct materials are 2 gallons at $4 per gallon. Last month, 11,200 gallons of direct materials that actually cost $42,400 were used to produce 6,000 units of product. The direct materials quantity variance for last month was

a. $3,200 favorable

b. $2,400 favorable

c. $3,200 unfavorable

d. $5,600 unfavorable

How do I solve this?

Thank you