Variances

Hi John sir, plz help me with the following question, The answer i find is quiet different and m confused.

A company operates std absorption costing system. The following information has been extracted from the standard cost card of one of its products:

Budgeted production 1,500 units
Direct materials cost: 7 kgs * $4.10 = $28.70 per unit

Actual results for the period were as follows:

Production 1600 units
Direct material ( purchased and used ) 1200 kgs, cost $52,200

It has subsequently been noted that, due to a change in economic conditions, the best price that the material could have been purchased for was $4.50 per kg during the period.

Find material price planning variance

I could not understand the solution , it takes 0.4 difference in price and multiplies it with 11200 units. 11200 UNITS are confusing me.