47x100-[9x(2502-10xa):3]+1781=3085
4700-[9x(2502-10xa):3]=3085-1781
4700-[9x(2502-10xa):3]=1304
9x(2502-10xa):3=4700-1304
9x(2502-10xa):3=3396
9x(2502-10xa)=3396x3
9x(2502-10xa)=11188
2502-10xa=11188:9
2502-10xa=1132
10xa=2502-1132
10xa=1370
a=1370:10
a=137
