Question

x+x\5=12 x-x\7=-3 x\5+x\2=21 5=5\7-3x

Answer 1

Ola Emanuela 

1) x + x/5 = 12

multiplique cada termo por 5

5x + x = 60

6x = 60

x = 10

2) x - x/7 = -3

multiplique cada termo por 7

7x - x = -21

6x = -21

x = -21/6 = -7/2

3) x/5 + x/2 = 21

mmc = 10

2x + 5x = 210

7x = 210

x = 30 

4) 5 = 5/7 - 3x

3x = 5/7 - 5 

3x = 5/7 - 35/7 

21x = -30

x = -30/21 = -10/7

Answer 2

X+x\5=12 5x +x = 60 ==> 6x=60==> x= 10======================================
x-x\7=-3==> 7x-x = - 21==>6x= -21==> x = - 21/6=============================================
x\5+x\2=21 ==>2x+5x=210==>7x=210==>x = 30===============================================5=5\7-3x ==>35 = 5 - 21x==>21x= 5-35==>21x=30==>x=30/35