Kostolom24 1)(x+240)*3-360=540
3x+720=900
3x=180
x=60
2)876+y+9869=78000
y=67255
3)a:30=768+987
a=30*(768+987)
a=52650

Asja2 (х+240)×3-360=540

(х+240)×3= 360+540
(х+240)×3= 900
x + 240 =900 : 3
x + 240 = 300
x = 300- 240
x=60

проверка:
(60 + 240) * 3 - 360 = 540
300 * 3 - 360 = 540
900 - 360 = 540
540 = 540

876+у+9869=78000
у =78000 - 876 - 9869
у = 77124 - 9869
у =  67255

проверка
876 + 67255 + 9869 = 78000
68131 + 9869 = 78000
78000 = 78000

а÷30=768+987
а÷30=1755
а = 1755 * 30
а = 52650

проверка:
52650 : 30 = 768 + 987
1755 = 1755