If Leila was half Miguel's age when Miguel was 6, Leila had to have been 3 years old. This tells you that Leila is 3 years younger than Miguel. Subtract 3 from 40 to get 37.
Step by step:A prediction is basically an educated guess and if you are looking for the exact word to describe that you would find that hypothesis is the correct way to tell what is a prediction.
