first of all to transfer (2x - 1)(x + 6) = 0 into a form where we can plug it into the quadratic formula we need to use the FOIL method.
(2x - 1)(x + 6) = 0
becomes
2x*x+2x*6+-1*x+-1*6
which simplifies to
2x^2 + 12x - x - 6
and then we add like terms to get
2x^2 + 11x - 6
now that it is in the correct form we can identify "a" "b" and "c" by following this form
ax^2 + bx + c
looking back at the equation we got earlier
2x^2 + 11x - 6
a=2,b=11,and c=-6