A) 208 + x = 389; x = 389 - 208 = 181;
б) 26 * 9 - x = 104; 234 - x = 104; x = 234 - 104 = 130;
в) x - 428 = 165; x = 165 + 428 = 593;
г) x + 480/8 = 570; x + 60 = 570; x = 570 - 60 = 510;
д) 639 - x = 27; x = 639 - 27 = 612;
е) 68/4 + x = 158; 17 + x = 158; x = 158 - 17 = 141;
з) x + 58 = 498; x = 498 - 58 = 440;
ж) x - 7*18 = 57; x - 126 = 57; x = 57 + 126 = 183.