What formula would be used to add two cells together after the equal sign?

Roger ginde is developing a program in supply chain management certification for managers. ginde has listed a number of activities that must be completed before a training program of this nature could be conducted. the activities, immediate predecessors, and times appear in the accompanying table: activity immediate predecessor(s) time (days) a -− 44b -− 55 c -− 11 d b 1010 e a, d 55 f c 55 g e, f 1010 calculate the slack time. show the details.