Which of the following is equal to the rational expression when x does not equal 3 or -10? (x+5)(x-3)/(x-3)(x+10)
a x+5/x-3
bx-3/x+10
cx+5/x+10
dx-3/x+5

For an expression to have a rational equivalent when solved, the denominator should not be equal to 0. If the denominator is equal to zero, the expression becomes indefinite or undetermined. This is the reason for the restriction of the use of x being equal to 3 or -10. 

In the given above, we can see that the expression x-3 appears both in the numerator and denominator. Hence, this can be cancelled. We are then left with the expression,
                (x + 5) / (x + 10)

Therefore, the answer to this item is letter C.