Correct answer is:

a) KaTeX parse error: KaTeX doesn't work in quirks mode. days

Explanation

Here,
Hours are inversely proportional to Days.
And,
Length, Breadth and Depth are Directly proportional to Days.
KaTeX parse error: KaTeX doesn't work in quirks mode.
KaTeX parse error: KaTeX doesn't work in quirks mode.
KaTeX parse error: KaTeX doesn't work in quirks mode. days.
Ans: If the workers dig a canal with a length of KaTeX parse error: KaTeX doesn't work in quirks mode. meters, breadth of KaTeX parse error: KaTeX doesn't work in quirks mode. meters, and depth of KaTeX parse error: KaTeX doesn't work in quirks mode. meters while working KaTeX parse error: KaTeX doesn't work in quirks mode. hours per day, it will take them KaTeX parse error: KaTeX doesn't work in quirks mode. days to complete the task.