a+b+c=77
a-7=3b
b+5=c/2
b=c/2 -5 = (c-10)/2
a= 3 (c/2 -5)= 3( c-10)/2= (3c-30)/2
(3c-30)/2 + (c-10)/2 +c =77 aducem la acelasi numitor
3c-30 +c -10 +2c = 154
6c -40=154
6c=154 +40
6c=194
c=194/6
a=(3 *194/6-30)/2= (194/2 -30)/2= (97-30)/2= 67/2
b= (196/6-10)/2= (196-60)/6/2= 136/6 *1/2= 68/6= 34/3