Problem $4$: Calculating the Number of Periods. For each of the following, solve for the unknown number of payments:

$\backslash$table$[[,$Present Value $($$$),$Years?,Interest Rate,Future Value $($$$),$Points$],[4$ a$,-740\mathrm{.}00,?,6\mathrm{.}00\%,900\mathrm{.}00,2\mathrm{.}5],[4b,900\mathrm{.}00,?,9\mathrm{.}00\%,1,500\mathrm{.}00,2\mathrm{.}5$