Variance

Hello, Sir. I'm here with another question. A company manufactures a single product. An extract from a variance control report together with relevant standard cost data is shown below. Standard direct material cost (10kg × $4 per kg) $40 per unit Actual results for January Total direct material cost $4,800 Direct material price variance $1,600 adverse Direct material usage variance $800 favourable The actual production in January was ………… units. __________________________________________ The formula that I know is [1] Actual Quantity x Actual Price = xxx [2] Actual Quantity x Standard Price = xxx [3] Standard Quantity x Standard Price = xxx ________________________________________ Price = [1] + [2] ; when [1] is lesser than [2] = Fav. Usage = [2] + [3] ; when [3] is lesser than [2] = Fav. Then, I thought "Total direct material cost $4,800" is the value of [1]. Therefore, I put $3,200 as [2]. Moreover, I brought down Std. P as $4/kg from the given and I got 800kg for Actual Quantity. However, it was totally wrong when I checked the answer which was 100. From this point, honestly, I'm not sure what this question is asking. Would you please explain step-by-step? Thank you very much.