How do I type the weighted-average cost formula into excel in order to get the correct number? So far, I have this: =(C10*E10)+(C11*E11)+(C12*E12)/SUM(C10,C11,C12). But the answer is incorrect.

In its first month of operations, McLanie Company made three purchases. Information concerning these purchases and units on hand are: Units on hand at period end 200 Purchases of merchandise were made in the sequence listed above