a+b=4
b+a+a=5, b+2a=5 b = 5-2a,
a+5-2a=4, -a=-1 , a= 1
b+2*1= 5, b =5-2, b= 3
c-d=2, c-6 =2, c =8
3+d=9, d = 9-3
ответ: a= 1, b =3 , c =8, d =6
a+b=4
b+a+a=5, b+2a=5 b = 5-2a,
a+5-2a=4, -a=-1 , a= 1
b+2*1= 5, b =5-2, b= 3
c-d=2, c-6 =2, c =8
3+d=9, d = 9-3
ответ: a= 1, b =3 , c =8, d =6