For a mine production t per year, the total cost of production is given by (at² + b). The revenue from sale is given by ct. If a, b and c, are constants, the breakeven value of t is

A. $$\frac{{\left[ {c \pm \sqrt {\left( {{c^2} - 4ab} \right)} } \right]}}{{\left( {2a} \right)}}$$

B. $$\frac{{\left[ {\sqrt {\left( {{c^2} - 4ab} \right)} } \right]}}{{\left( {2a} \right)}}$$

C. $$\frac{{\left[ { - c \pm \sqrt {{c^2} - 4ab} } \right]}}{{\left( {2a} \right)}}$$

D. $$\frac{{\left[ {c \pm \sqrt {{c^2} - 4ab} } \right]}}{{\left( {2a} \right)}}$$

Answer: Option A