a+ b= 23400
2(a-1800)= b+ 1800
2a- 3600= b +1800
2a= b+ 1800+3600
2a= b+ 5400
a= b:2 + 2700
b:2 + 2700 + b = 23 400 (multiplicam ecuatia cu 2)
b + 5400 + 2b= 46 800
3b= 46 800 - 5 400
3b= 41 400
b= 13 800
In a doua biblioteca gasim 13 800 carti
In prima biblioteca gasim 23 400 - 13 800 = 9 600