Expanded notation can be defined as to rewrite the numbers to show their place values
For example in the given question 3 is at the tenth thousand place, 1 is at the thousand'th place,8 at tenth and 4 at unit place so the solution for the question is given below:
Since there are 6 black dogs and 5 white dogs, there is 11 black and white dogs. There is 15 dogs in total, so you subtract 11 from 15, and that is 4. So, 4 dogs are blue.
