The way I would read it is as the following:
The fraction of Vishal's monthly income that he invested in stocks was 2/11, and the fraction he invested in mutual funds was 4/11.
If the author prefers to include "that of," perhaps he'd word it like this:
The fraction of Vishal's monthly income that he invested in stocks was 2/11, and that of mutual funds was 4/11.
The word "that" in the phrase is referring to the subject, such as when the author asked this question (8):
The ratio of investment of A and B is 7 : 8 and that of B and C is 4 : 9.
The subject of the sentence is "ratio of investment," so it reads, "and [the ratio of investment of] B and C is 4:9." The subject in the question you're asking about, however, is Vishal, hence the confusion.
Another possibility is that "that" is referring to the 2/11th part. This is more complex, which is why I don't think it's the intended meaning, but it could have the following meaning:
Vishal invested 2/11th part of his monthly income in stocks, and even the money for that investment he had taken out of 4/11 part of his mutual fund investments.
If you drill down on what sort of real actions Vishal would be taking, in this case, it becomes a strain to follow logically, such that Vishal is funding his investments in stocks with a fraction of his mutual fund investments, so he's selling some of those, apparently, yet his stock purchases are said to be coming out of his monthly income. Is this a contradiction, or is his monthly income coming from his mutual fund investments? Argh!
To make a short story long, I'd go with the first reading.