correct answer is: b) KaTeX parse error: KaTeX doesn't work in quirks mode.

Explanation

Here,
The given relation is KaTeX parse error: KaTeX doesn't work in quirks mode.
Or, 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.
KaTeX parse error: KaTeX doesn't work in quirks mode.
So that, in the relation the KaTeX parse error: KaTeX doesn't work in quirks mode. value is KaTeX parse error: KaTeX doesn't work in quirks mode.
Ans: KaTeX parse error: KaTeX doesn't work in quirks mode. value is KaTeX parse error: KaTeX doesn't work in quirks mode.

Another method to articulate this particular math query is available:

1. Calculate the value of x in the relation 4 : 7 = 12 : x.
2. Find the unknown value x in the proportion 4 : 7 = 12 : x.
3. If the ratio 4 : 7 is equal to the ratio 12 : x, what is the value of x?