Which one of the following is a square root of $-\sqrt{-1} $?

What is the maximum number of points of intersection of 10 circles?

A set S contains (2n + 1) elements. There are 4096 subsets of S which contain at most n elements. What is n equal to?

If $\left|\begin{array}{ccc} x^2+3 x & x-1 & x+3 \\ x+1 & -2 x & x-4 \\ x-3 & x+4 & 3 x \end{array}\right|$ = ax4 + bx3 + cx2 + dx + e, then what is the value of e?"