t=t1+t2
t1=S/2:v1
t2=S/2:v2
v=S/t=S/(S/2:v1+S/2:v2)=S/(S/2:(8*v2)+S/2:v2)
v=S/(S/2:(8*v2)+S/2:v2)
v*(1/2:(8*v2)+1/2:v2) = 1
v*(1/(16*v2)+1/(2:v2)) = 1
v*(1/16+1/2) =v2
v2=v*(8/16+1/16)=v*9/16=16*9/16 км/час = 9 км/час - это ответ
t=t1+t2
t1=S/2:v1
t2=S/2:v2
v=S/t=S/(S/2:v1+S/2:v2)=S/(S/2:(8*v2)+S/2:v2)
v=S/(S/2:(8*v2)+S/2:v2)
v*(1/2:(8*v2)+1/2:v2) = 1
v*(1/(16*v2)+1/(2:v2)) = 1
v*(1/16+1/2) =v2
v2=v*(8/16+1/16)=v*9/16=16*9/16 км/час = 9 км/час - это ответ