Question

calcule o valor de x nas eguaçoes -8x-21=54-5x b) 5(2x-3) = 7x-40

Answer 1

a)-8x-21=54-5x

-8x+5x=54+21

-3x=75 (-1)

3x=-75

x=-75/3

x= -25

b)10x-15=7x-40

10x-7x=-40+15

3x=-25

x= -25/3

Answer 2

Ola amigo

Questão a)

-8x-21= 54-5x
-8x+5x= 54+21
-3x= 75
x= $\frac{75}{-3}$= -25

Questão b) 

5 (2x - 3)= 7x - 4
10x -15 = 7x - 4
10x - 7x= -4+15
3x= 11
x= $\frac{11}{3}$