Technically there is not enough information to answer the question, not unless we assume that every person speaks either hindi, english or both. It's entirely possible that 40 people all speak both hindi and english, 35 people speak hindi only and the remaining 25 speak some other language.

But let's assume that's not the case.

My advice when creating a venn diagram is to always start in the middle and work your way out.

So then, you know that you have 2 bubbles with some overlap.

in the first bubble there should be 40 and in the second bubble there should be 75 and combined there should be 100.

but we have a total of 40 + 75 = 115 people who speak either english or hindi, which means that we double counted 115 - 100 = 15 times.

Because. since there are only two bubbles, there is no other way we could have gotten more than 100 total.

If we had three bubbles, then it would be a bit more complicated, because we would have to figure out whether we double or triple counted those extra 15.

But in this case we found that the middle number of the venn diagram should be 15. So, then we start to work our way out.

Now for the English bubble, we know that we should have a total of 40 people, but we already know that there was an overlap of 15 people.

Then, there are two ways that we can solve this:

1.) 40 people speak English, and 15 people speak both, so the total number of people who speak only English must be 40 - 15 = 25.

OR

2.) We have a total of 100 people, and 75 people speak either hindi or both. So, the number of people who speak only english should be the same as the number of people who do not speak hindi, ie. 100 - 75 = 25.

And now that we know how many people speak only english and how many people speak both, there are 3 ways to find how many people speak only hindi (which should be the last remaining bubble to fill in).

1.) we know that the total number of people who speak hindi is 75, and the total number that speak both is 15. So, we take the difference, 75 - 15 = 60 people.

OR

2.) We know that the total number of people questioned was 100. And the number of people who speak English was 40. So, we take the difference 100 - 40 = 60 people who speak only hindi, or people who do not speak english. In this case those two things are one in the same.

OR

3.) We know that the total number of people questioned was 100. And we have one unfilled bubble left. So we start with 100, and subtract what's already filled in to the other bubbles, which should give us 100 - 15 - 25 = 60 people.