The answer is -7. I got my answer by first facoring 49 to get 7². Next, I applied a radical rule. In your case, √7² =7 because 7x7 = 49 and so √49 = 7. The answer is - 7 however because you have a negative symbol in front of the radical.
I hope that my wording doesn't sound too confusing! Let me know if it does.