Răspuns:
Explicație pas cu pas:
5a-4b+7c-d=308
a/13=b/11=c/9=d/7=k
a=13k
b=11k
c=9k
d=7k
5*13k-4*11k+70-7k=308
65k-44k-7k=308-70
14k=238 => k=238/14=17 => k=17
a=13*17=221
b=11*17=187
c=9*17=153
d=7*17=119
verificare:
5*221-4*187+70-119=308
1105-748+70-119=308
308=308