First, rewrite the given expression 6s + 18s as 6s² + 18s = 0 to get it into standard quadratic form ax² + bx + c = 0. Then factor out the greatest common factor, which is 6s, resulting in 6s(s + 3) = 0. Set each factor equal to zero: 6s = 0 gives s = 0, and s + 3 = 0 gives s = -3.