Does anyone have any clue what these questions are asking for? This doesn't make sense to me, and I can't find this notation in my text. Thanks.

(a) Determine $\displaystyle Q_{240}$

(b) Determine $\displaystyle T(U_{240})$

(c) Find all solutions of $\displaystyle x^2 \equiv$ -23 (mod 240)

Thanks in advance!

A walk through would be great.