What is the sum of all values of y for which the expression (y + 6)/(y^2 - 8y + 2) is undefined?

Any vlue of 'y' that makes the denominator will result in an 'undefined' situation

y^2 -8y+2 = 0

The sum of the roots can be found by -b/a = 8

....or you can use the quadratic formula to find roots x = 4 +- sqrt(14) sum = 8