DAX:The SUMX function

When do you need the SUMX() function? Easy question but more difficult to answer. One of my current projects is about analyzing the sales data with the PQM analysis. What is PQM analysis, I hear you say? Well, PQM stands for Price, Quantity Mix analysis or sometimes it's called PVM analysis: V for Volume. And one of the calculations that needs to be done is calculating the Sales amount based on Quantity Sold and Price per Unit. S