This is because according to the all the numbers we have, all they did was divide the numbers from the bigger triangle by 2. So, 10 divided by 2 is equal to 5. That is where the 5 came from. 7 divided by 2 is equal to 3.5. That is where the 3.5 came from. 6 divided by 2 is equal 3. That is why y is equal to 3.
Hope this helps, have a great day, stay safe and positive.
