a+b+c+d=138
(a+2+2+2)+ (b-2)+c-2)+(d-2)=138
=> a+6; a+7; a+8; a+9
b-2=a+7 => b=a+9
c-2=a+8 => c=a+10
d-2=a+9 => d=a+11
a+b+c+d=a + a+9 + a+10 + a+11=138
4a+30=138
a=(138-30):4
a=108:4
a=27; b=36; c=37; d=38
din a+2+2+2 ; b-2; c-2; d-2
=> 33; 34; 35; 36