First: 240km/1hour=120km/?hour
Cross multiply and divide
(120*1)/240= 0.5hour
Second: 220km/1hour=120km/?hour
Cross multiply and divide
(120*1)/220=0.545hour
Third: 210km/1hour=120km/?hour
Cross multiply and divide
(120*1)/210= 0.571hour
Fourth: 205km/1hour=120km/?hour
Cross multiply and divide
(120*1)/205= 0.585hour
Fifth: 200km/1hour=120km/?hour
Cross multiply and divide
(120*1)/200= 0.6hour