Please help me with this question :)​

At the newest animated movie, for every 9 children, there are 4 adults. there are a total of 39 children and adults at the movie.

How can i differentiate this equation?

Margaret is purchasing a house for $210,000 with a 15 year fixed rate mortgage at 4.75% interest she has made a 5% down payment the house is valued at 205,000 and the local tax rate is 3.5% homeowners insurance 600 per year what are her total monthly payment