Б) 819 + 153 = 819 + (1 + 152) = (819 + 1) + 152 = 820 + 152 = 972
д) 305 + 239 = (304 + 1) + 239 = (239 + 1) + 304 = 240 + 304 = 544
з) 893 + 98 = (891 + 2) + 98 = 891 + (2 + 98) = 891 + 100 = 991
л) 325 + 3997 = (322 + 3) + 3997 = 322 + (3 + 3997) = 322 + 4000 = 4322