[23 − (4 · 2 + 5 · 2)][(5 · 6 − 4) − 21]

Ok, well, 25 is as simple as it gets (assuming you mean the dot to represent multiplication)!

Do you mean [23 - (4*2 + 5*2)]*[5*6 - 4 - 21] = (23 - 18)*(30 - 25) = 5*5 = 25 ? 

Sorry I didn't clarify.  I would just like that expression simplified.

Thank you, sir!