You could factor the function, and solve for x, this one happens to factor easily.
x^2 - 11x - 8x + 88
(x - 8)(x - 11) = 0
x - 8 = 0
x = 0 + 8
x - 11 = 0
x = 0 + 11
There are your two x-coordinates.
x^2 - 19x + 88 = 0
or you could just plug in the values into the quadratic equation, the function is already in standard form.
a = 1
b = -19
c = 88
Just a note when entering the values, keep each value in a bracket with the original sign from the equation outside of the bracket.
for example the first b value that shows up in the situation would be -b, which when the values are plugged in would be -(-19), which is 19.