(х+51)*309=16686  
9435/(77-x)=555 

(х+51)*309=16686х+51= 16686:309х+51= 54х= 54-51х=3_______(3+51)*309=16686 16686=166869435:(77-х)=55577-х=9435:55577-х=17х=77-17х=60________9435:(77-60)=555 555=555