1. 100520-470*50+13980=91000
470*50=23500 100520-23500=77020 77020+13980=91000
2. 14110+801000:900-7604=7396
801000:900=890 14110+890=15000 15000-7604=7396
3. 734600:50+454*40=32852
734600:50=14692 454*40=18160 14692+18160=32852
4. (560-12240:30)+145=297
12240:30=408 560-408= 152 152+145=297