√x - 6√x = 1
Multiply through by √x
x - 6 = √x
x - √x = 6
let √x = q, then x = q2
q2 - q - 6 = 0
q2 - 3q + 2q - 6 = 0
q(q - 3) + 2(q - 3) = 0
(q - 3)(q + 2) = 0
q = 3 or -2
but x = q2, meaning, x = 9 or 4.