Sheridan Creations purchased 8500 feet of copper tubing at a price of $2.30 per foot and used 8200 feet during the period. The standard quantity allowed for the units produced is 8000 and the standard price of the copper tubing is $2.60 per foot. What is Sheridan Creations' direct materials quantity variance for the period? $520 unfavorable $780 unfavorable $1300 unfavorable 5460 unfavorable