List all elements of the domain of the function {(-3,,,-,-,4)}.

If I am not mistaken the domain should be [-3, 5, -9, 7, 6].

The domain is the numbers that you can use, normally the x values
(x,y)
so just list all the first numbers in each pair, ignore repeats

so
-3,5,-9,7,6
and people like to order them so
D=[-9,-3,5,6,7]

17 is c. congruent means equal in size

Subtracting is the opposite of adding