You wish to qualify for a $200,000 mortgage. Your monthly payment (principal and interest) must not exceed 25% of your monthly income. Your monthly payment plus taxes and homeowners insurance must not exceed 28% of your monthly income. Your monthly payment, taxes, insurance, and other debt payments must not exceed 33% of your monthly income. The loan is for 30 years. Interest rates for these loans are 7%. Taxes and insurance are $250 per month and you have a $300 car payment. Which of the following best describes how high your monthly income needs to be for you to qualify?

Please just tell me how to calculate monthly principal payment and monthly interest payment on average. I already know how to do the rest.