Determine the sum of is a phrase used to describe the process of calculating the TOTAL amount of something. This can be done by adding, totaling, assessing, or assaying the items in question. Adding involves combining two or more numbers together to get a sum. Totaling is the process of finding the sum of all the items in a set. Assessing is the act of evaluating the value of something. Lastly, assaying is the process of analyzing and evaluating a substance or material.