Although the square root in the answer may seem intimidating, this question is easier than it seems. The main thing to know to solve this problem is the quadratic equation (used to factor and find values of x that will set the function equal to 0), which is shown below.
A, b, and c correspond to the coefficients of the function, so a=1, b=-10, and c=14. If we plug in 1 for a, -10 for b, and 14 for c, we get (10+√(100-56))/2. This simplifies to (10+√44)/2. We can expand √44 into √11 x √4 (which simplifies to 2). We now have (10+2√11)/2, and if we divide everything in the numerator by two we get 5+√11, so 11 is the answer.