How do you find square roots and then find the exact distance the square root is ? (I don’t know if I wrote it right or not but does anybody know it would be a BIG help to me)

The function y= x - 4x+ 5 approximates the height, y, of a bird, and its horizontal distance, x, as it flies from one fence post to another. all distances are in feet. complete the square to find and interpret the extreme value (vertex). select two answers: one extreme value and one interpretation.