The CUMPRINC() function is similar to the CUMIPMT() function, except rather than calculate the cumulative interest paid, the function calculates the cumulative principal paid in a period of time. You have a mortgage loan at 6% over 30 years for $150,000. (a) Use Goal Seek to find the approximate period in which $5000 in principal payments have been accumulated. (b) Use Goal Seek to find the approximate period in which $75,000 in principal payments have been accumulated. (c) If the use of Goal Seek is problematic for problem 11b, what do you suggest as an alternative to finding the approximate period that still uses the CUMPRINC() function?