Cardinal uses the high-low method of estimating costs. Cardinal had total costs of $25,150 at its lowest level of activity, when 6,400 units were sold. When, at its highest level of activity, sales equaled 12,100 units, total costs were $39,970. Cardinal would estimate variable cost per unit as: OOO O $2.60 O $3.30 $3.52 $3.93