8.

1. 648720:68+506-108-63295 = 9540 + 506 - 108 - 63295 = -53357

2. 608-506-236-400+8716 = 102 - 236 - 400 + 8716 = 8182

3. 286996:(1010-553)+164268:324 = 286996:457 + 507 = 628 + 507 = 1135

4. 1000000-(700800+425*704)+25 = 1000000-(700800+299200)+25 = 1000000-1000000+25 = 25