I think the 4th one but Im not too sure please forgive me if I'm wrong.
Since the formula for the area of a circle is Pi x r squared, the area would be 81 x Pi (you teacher may want you to use Pi as 3.14 or put it in your calculator).
12x2-7=6-2x2+2
14x^2-15=0
a=14 , b =0 , c=-15
0^2-4x14x(-15) =
840
