How Do I Solve 6x2 + 3x – 18 = 0 Using The Quadratic Formula?

The quadratic formula is -b +/- The square root of b squared - 4ac divided by 2a.

Assuming that first number is 6x squared, a=6, b=3. And c= -18

To work this problem you would say:
-3 +/- the square root of 3^2 - 4(6)(-18) divided by 2(6)
-3 +/- the square root of 9 + 432 divided by 12
-3 +/- the square root of 441 divided by 12
-3 +/- 21 divided by 12
-3 +/- 1.75
-4.75 and -1.25 are the answers

The quadratic formula says that the solutions to
  ax² + bx + c = 0
are given by
  x = (-b ±√(b² - 4ac))/(2a)

You have
  a = 6, b = 3, c = -18, so we can put these into the formula as follows...
  x = (-3 ±√(3² - 4*6*(-18)))/(2*6)
  = (-3 ±√(9+432))/12
  = (-3 ±√441)/12
  = (-3 ± 21)/12
  = {-24/12, 18/12}
  = {-2, 1 1/2}

The two solutions are  x = -2  and  x = 1 1/2.