Hey there !
The Sum is basically addition
Of two numbers, that is a number and 12.
We don't know what your unknown number is so will put it as "X"
and 12 = 12
Therefore, [tex]12 + x [/tex] (option C) would mostly be your result because it is the sum of those two numbers
Good luck on your assignment and enjoy your day!
~[tex]LoveYourselfFirst:)[/tex]