Answer:
You need to invest $183.3 in a stock with an annual return of 15% so that the return on the total investment is 12%.
Step-by-step explanation:
Consider the provided information.
You have already invested $550 in a stock with an annual return of 11%. The interest earn will be: 
Let x amount invested at 15%, the interest earn will be: 
It is given that we want that the return on the total investment is 12%
This can be written as

Now solve the above equation for x.





Hence, you need to invest $183.3 in a stock with an annual return of 15% so that the return on the total investment is 12%.