t=t1+t2
t1=d/(v+c)
d1'=v*t1
d1''=v*t1
d1'=d1''=v*t1
d1=d-d1'-d1''=d-2v*t1=d-2vd/(v+c)=d(1-2v/(v+c))
t2=d1/(v+c)=d(1-2v/(v+c))/(v+c)
t1+t2=t=d/(v+c)+d(1-2v/(v+c))/(v+c)=[d+d(1-2v/(v+c))]/(v+c)=d(2-2v/(v+c))=>d=t(v+c)/(2-2v/(v+c))=68(160+340)/(2-2*160/(160+340))=68*500/(2-320/500))=34000/(2-0,64)=34000/1,36=25000 m=25 km