Explanation:
are you sure this is the whole information ?
because
6² = 5x + 6
is not called a quadratic equation.
it is a quadratic equation, when there is one term in x² involved.
I assume therefore, that your problem is
6x² = 5x + 6
that is then as basic quadratic equation
6x² - 5x - 6 = 0
the general solution to a quadratic equation is
x = (-b ± sqrt(b² - 4ac))/(2a)
a = 6
b = -5
c = -6
x = (5 ± sqrt((-5)² - 4×6×-6))/(2×6) =
= (5 ± sqrt(25 + 144))/12 = (5 ± sqrt(169))/12 =
= (5 ± 13)/12
x1 = (5 + 13)/12 = 18/12 = 3/2
x2 = (5 - 13)/12 = -8/12 = -2/3
so, the 2 solutions for the quadratic equation are
x = 3/2 and x = -2/3