中一英文數學應用題(1題,急!10點)

Kelvin can cycle 12km every hour and run 5km every hour. He starts from his home and cycles eastwards for 1 1/2 hours. Then he runs westwards for 1/2 hours. After taking a rest, he jogs 5km westwards. Suppose that positive numbers represent positions on the east of his home. Use a directed number to represent his final position.

答案係10.5KM. 我要步驟同式 THX!