correct answer is: c) 80 km

Explanation

Let, he travelled KaTeX parse error: KaTeX doesn't work in quirks mode. km overall.
Now, KaTeX parse error: KaTeX doesn't work in quirks mode. of his journey he travelled by train.
KaTeX parse error: KaTeX doesn't work in quirks mode. The man travelled by train KaTeX parse error: KaTeX doesn't work in quirks mode. km.
KaTeX parse error: KaTeX doesn't work in quirks mode. km.
Now, KaTeX parse error: KaTeX doesn't work in quirks mode. of journey he travelled by bus.
KaTeX parse error: KaTeX doesn't work in quirks mode. The man travelled by bus KaTeX parse error: KaTeX doesn't work in quirks mode. km.
KaTeX parse error: KaTeX doesn't work in quirks mode. km.
And now, KaTeX parse error: KaTeX doesn't work in quirks mode. km he travelled by foot.
So that, The man total travelled KaTeX parse error: KaTeX doesn't work in quirks mode. km.
KaTeX parse error: KaTeX doesn't work in quirks mode. km.
KaTeX parse error: KaTeX doesn't work in quirks mode. km.
According to the question,
KaTeX parse error: KaTeX doesn't work in quirks mode. km
KaTeX parse error: KaTeX doesn't work in quirks mode. km _{[cross multiply]}
KaTeX parse error: KaTeX doesn't work in quirks mode. km _{[interchange]}
KaTeX parse error: KaTeX doesn't work in quirks mode. km
KaTeX parse error: KaTeX doesn't work in quirks mode. km
KaTeX parse error: KaTeX doesn't work in quirks mode. km
KaTeX parse error: KaTeX doesn't work in quirks mode. The man travelled overall KaTeX parse error: KaTeX doesn't work in quirks mode. km.
Ans: Overall the man travelled 80 km.

Another form of this specific math question exists:

1. A man traveled fractions of his journey by train and bus, and walked the rest, totaling 18 km. How far did he travel in total?
2. Find out the entire journey distance when a man covered 3/8 by train, 2/5 by bus, and the rest by foot with the remaining distance given as 18 km.
3. Calculate the total distance traveled by a man who completed 3/8 of his journey by train, 2/5 by bus, and the remaining 18 km on foot.