Hi Kannan,
There is an error in your equation.
It should be,
$$\ 12+\frac{60}{100}\left(x-40\right)=\frac{50}{100}\left(x\right)$$
$$\ \frac{x}{10}=12$$
x = 120
This means he players 80 more matches later.
It is given, 90% matches are won, i.e. 72 more matches are won.
Total matches won = 12 + 72 = 84
Hope this helps!

it is easier to go by options in this question

Got it ma'am thank you for the clarrification

Hi Himanshi,
The remaining matches are not the matches included in the initial 40 matches. There are matches other than these 40 matches, and the extra information given in the question about the team winning is about those other matches. Out of these 40, the team only won 30% of them and lost 70% of them. We do not know the total number of matches played, and it is not 40, so we must calculate the number using the information in the question.
Hope this helps!