t1=3 min 20 s=200 s
d=7 km=7000 m
t2=23 min 20 s=1400 s
x1=v1t1
x2=d-v2t1
x1=x2=>(v1+v2)t1=d=>v1+v2=d/t1=7000/200=35=>v1+v2=35
x2'=v2t2
x1'=-d+v1t2
x1'=x2'=>v2t2=-d+v1t2<=>(v2-v1)t2=-d=>v2-v1=-d/t2=>v2-v1=-7000/1400=5=>v2-v1=-5=>v1=5+v2
5+2v2=35=>2v2=30=>v2=15 m/s
v1=5+v2=5+15=20 m/s