12. Resolver
(1):3/x+1 - 1/y+1=7
(2):1/x+1- 1/y+1=13

(1):3(x+1)-1(y+1)=7
3x+3-y+1=7
3x-y=7-3
3x-y=5
(2):1(x+1)-1(y+1)=13
x+1-y-1=13
x-y=13-1+2
x-y=13
Indicar el valor de "x"
3x-y=5
-
x-y=13
2x=8
x=8/2
x=4
​