You can simply apply the formula for solving a quadratic equation, but you'll need a calculator, judging by the awkwardness of the numerical coefficients. The standard quadratic is usually written ax^2+bx+c=0. In your question a=-4.905, b=1.85, c=69.3. The formula is (-b+/-sqrt(b^2-4ac))/2a, where I've used +/- to mean plus-or-minus so that two different solutions are possible, one using the positive square root and the other using the negative one. Substituting in the formula the two solutions are:
(-1.85+sqrt(3.4225+4*4.905*69.3))/-9.81 = -3.5749 and
(-1.85-sqrt(3.4225+4*4.905*69.3))/-9.81=3.9521.