x+12/5 = 12 - x/10 - 4 - x/2
x+x/10+x/2 = 12 -4-12/5
(10x+x+5x)/10 = (120-40-24)/10
10x+x+5x=120-40-24
16x=56
x=56/16
x=7/2
(x=3,5)

pte verif :
7/2 + 12/5 = 59/10
12 - 7/20 - 4 - 7/4 = 59/10
ok.