74
б) 198 * 16 - 98 * 16 = (198 - 98) * 16 = 100 * 16 = 1600
в) 248 * 65 + 31 * 65 - 279 * 64 = (248 + 31) * 65 - 279 * 64 = 279 * 65 - 279 * 64 = 279*(65 - 64) = 279 * 1 = 279
г) 28 * 51 - 17 * 51 + 11 * 49 = (28 - 17) * 51 + 11 * 49 = 11 * 51 + 11 * 49 = 11 * (51 + 49) = 11 * 100 = 1100