Respuesta :
1 1/2 I believe is your answer. I really don't know if this is correct or not. Sorry if I am wrong.
(12+x)/(13-x)=3/2
2(12+x)=3(13-x)
24+2x=39-3x
5x=15
therefore x=3
Test it out
(12+3)/(13-3)= 15/10= 3/2
2(12+x)=3(13-x)
24+2x=39-3x
5x=15
therefore x=3
Test it out
(12+3)/(13-3)= 15/10= 3/2