Answer: Vw = 2.23 km/h
Explanation:
(V0 + Vw)t1 = d
(V0 - Vw)t2 = d
t = t1 + t2
where d = 10 km and t = 5 h
From the first three equations we have:
d/(V0 + Vw) + d/(V0 - Vw) = t ( I inserted t1 and t2 into the third equation)
(d(V0 - Vw) + d(V0 + Vw)) / V0² - Vw² = t
(dV0 - dw + dVo + dVw) / Vo² - Vw² = t
(2×d×V0) = t(V0² - Vw²)

Vw = 2.23 km/h