We require that the expression under the radical, the "radicand",
is not negative, but is 0 or something greater.
The expression on the left has zeros 3 and -3, so we
mark these solid on a number line:
-------------@-----------------------@--------
-6 -5 -4 -3 -2 -1 0 1 2 3 4 5
We choose a test value on the left of -3, say -4, and
substitute it in:
This is false so we do not shade to the left of -3
So we still have:
-------------@-----------------------@--------
-6 -5 -4 -3 -2 -1 0 1 2 3 4 5
We choose a test value between -3 and +3, say 0, and
substitute it in:
This is true so we shade the part of the number line between
-3 and +3 inclusive of -3 and 3 since the inequality is 
and not >. So we have:
-------------@=======================@--------
-6 -5 -4 -3 -2 -1 0 1 2 3 4 5
We choose a test value on the right of +3, say +4, and
substitute it in:
This is false so we do not shade to the right of 3
So we still have:
-------------@=======================@--------
-6 -5 -4 -3 -2 -1 0 1 2 3 4 5
and the domain is [-3,3]
The integers in the domain are -3, -2, -1, 0, 1, 2, 3.
So the answer is 7, choice d.
Edwin
