Question

срочно!!!!!!!!!!!!!!!!!!!!!

Answer 1

S=x
t=S/V
t1=1/3x:20
t2=1/3x:5
t3=1/3x:80
1/3x*1/20+1/3x*1/5+1/3x*1/80=4
x/60+x/15+x/240=4/1
4x/240+16x/240+x/240=4/1
21x/240=4/1
21x=960|:21
x=960/21=320/7=45 5/7км