8x - (x + 3) = 11

8x - x - 3 = 11

8x - x = 11 + 3

7x = 14

x = 14/7

x = 2

100x + 80x = 120x - (40x - 300)

100x + 80x = 120x - 40x + 300

100x + 80x - 120x + 40x = 300

220x - 120x = 300

100x = 300

x = 300/100

x = 3

Olá, boa noite ☺

Resoluções:

a)

8x - (x + 3) = 11

8x -x - 3 = 11

7x - 3 = 11

7x = 11 + 3

7x = 14

x = 14/7

x=2

b)

100x+80x=120x-(40x-300)

100x + 80x = 120x - 40x + 300

100x + 80x - 120x + 40x = 300

100x=300

x=300/100

x=3

Bons estudos :)