This quadratic should be solved using the quadratic formula.
The quadratic formula is
(-b +/- sqrt(b2 - 4ac)) / (2a) (Side note: The +/- means that you use the plus sign once, then recalculate again using the minus sign. You should get two answers this way.)
The numbers that we plug into the letters can be found from the general form of a quadratic equation
ax2 + bx + c
In your quadratic a = 3, b = 1, and c = -5. I'll let you try and solve the rest on your own. Whatever your answer is, round it off to two decimal places.