Răspuns :
100-[400-(28·c-2)·7]=123-45=>78;
400-(28·c-2)·7=100-78=>22;
(28·c-2)·7=400-22=>378;
28·c-2=378:7=>54;
28·c=54+2=>56;
c=56:28;
c=2.
notam (28c-2)=a
100-(400-a*7)+3*15=123
100-(400-7a)+45=123 notam (400-7a)=b
100-b+45=123
-b=123-145
b=22 inlocuim
400-7a=22
-7a=22-400
-7a=-378
a=378/7
a=54 inlocuim
28c-2=54
28c=54+2
28c=56
c=56/28
c=2
100-(400-a*7)+3*15=123
100-(400-7a)+45=123 notam (400-7a)=b
100-b+45=123
-b=123-145
b=22 inlocuim
400-7a=22
-7a=22-400
-7a=-378
a=378/7
a=54 inlocuim
28c-2=54
28c=54+2
28c=56
c=56/28
c=2