Question

which key combination is used to get the total of adjacent cells

Answer 1

=sum(firstcell:lastcell)

Answer 2

"     The reference in which the question has been asked is not specified. On assuming that the question has been asked in reference to the Microsoft Excel which is included in the Microsoft Office package.

     So, in it, the key combination which is "used to get" the "total of adjacent cells" is "Alt+=". Or as an alternative, one can use and excel formula using the SUM() function whose syntax is SUM(firstcell:lastcell)."