Black to move:
[fen "4rbk1/pp3pp1/1nq4p/8/1PP5/P3N1P1/Q2BrP1P/3R1RK1 b - - 0 1"]
I've tried to solve this chess problem - black to move, find the best move. I couldn't work it out so I checked the solution, which was R8xe3. I don't understand why this is the best move - could someone explain please?