126+(98+274)=(126+274)+98=400+98=498
900-305=900-(300+5)=900-300-5=600-5=595
924-(275+324)=924-275-324=(924-324)-275=600-275=325
926-498=926-(500-2)=926-500+2=426+2=428
837-399=837-(400-1)=837-400+1=437+1=438
758-297=758-(300-3)=758-300+3=458+3=461
643-599=643-(600-1)=643-600+1=43+1=44