Răspuns:
Explicație pas cu pas:
a-b = 6
a) x+3a-3b=20
x+3(a-b) = 20
x+3*6=20, x=20-18, x= 2
b) xa-xb+9a-9b=654
x(a-b)+9(a-b)=654
(a-b)(x+9)=654
6(x+9)=654/:6
x+9=109, x=109-9, x=100
c) 7a-7b+x=55
7(a-b)+x=55
7*6+x=55, 42+x=55
x=55-42, x=13
d) 13+x-(5a-5b)=2011
13+x-5(a-b)=2011
13+x-5*6=2011
x+13-30=2011,
x=2011-13+30
x= 2028