Пж помогите !!!!!!!!!!!!!!!!

1. а)
$52 + 19 + 31 + 48 = (52 + 48) + (19 + 31) = 100 + 50 = 150$
б)
$835 + 431 + 165 + 119 = (835 + 165) + (431 + 119) = 1000 + 550 = 1550$
2. а)
$48665247 + 9958296 = 58623543$
б)
$4687 + 51 + 2017 = 6755$
3. а)
$534 - x = 255 \\ x = 534 - 255 = 279 \\ 534 - 279 = 255$
б)
$x - 755 = 5678 \\ x = 5678 + 755 = 6433 \\ 6433 - 755 = 5678$
в)
$x - 765 = 8906 \\ x = 8906 + 765 = 9671 \\ 9671 - 755 = 8906$