THE ANSWER IS 21. I just want to know if someone knows the solution and if possible using TVM calculator. Thank you.

A $120,000 mortgage with an interest rate of 4.9 percent compounded semi-annually has a monthly payment of $700.13 for 21.0 years. Calculate the number of years to pay off the mortgage if payments are made on an accelerated biweekly basis instead of monthly. It will require years to pay off the mortgage if payments are made on an accelerated biweekly basis. (Round to one decimal place.)