prima etapa⇒2/7·y=2y/7;
a ramas y-2y/7=7y/7-2y/7=5y/7;
a doua etapa⇒1/4·5y/7=5y/28;
a ramas 5y/7-5y/28=20y/28-5y/28=15y/28;
a treia etapa⇒1/3·15y/28=1/1·5y/28=5y/28;
a ramas 15y/28-5y/28=10y/28;
⇒10y/28=200
⇒y=28·200/10
⇒y=28·20
⇒y=560km[lungimea intregului drum];