Hi there! 5x²-45=0, add 45 to both sides, 5x²-45+45=0+45=5x²=45. Divide both sides by 5, 5x²/5=45/5, 45/5=9. So, we have x²=9. we have to find the square root of 9. The square root of 9 is 3*3 because 3*3=9. We have two solutions, the first solution is x=3 and the other solution is x=-3. X=3 and x=-3 can be combined and we get {3,-3}. Therefore, your answer is B. {3,-3}