How would I solve this in Excel?

b. You also want to save for retirement. In cell B12, enter a formula to calculate how much you will have saved by putting away that same $400 per month for 25 years at 4%. Use the appropriate cell references. Remember to use a negative value for the Pmt argument and to adjust the Rate and Nper arguments to reflect monthly payments. There is no money in the account yet and payments are applied at the end of every month, so omit both the Pv and Type arguments. (Hint: Use the FV function.)