in problem 6, how and why did we get N=60?

Problems 4-9 are based on the following information: You've just took a 20-year $300,000 mortgage with monthly interest rate of 0.3%. Based on this information, you found that your monthly payments are $1,755.33 Problem 4: How much of your FIRST monthly payment will go toward the interest payment? 300000*0.003-$900 Problem 5: How much of your SECOND monthly payment will go toward the interest payment? (300000+900-1755.33)*0.003-$897.43 Problem 6: What will be your mortgage balance in 15 years (right after you make your 180 payment)? 1-03; N-60; PMT-1755.33; CPT PV. Find PV-96253.34