His first payment was at the end of January in which his son started Grade $1$ and the last payment at the end of December when his son completed his Grade $12.$ His son did not repeat any grade.

He withdrew all his savings one month after his last payment.

Calculate the amount that was in his account by the time Mr Duda withdrew all the savings.

$6\mathrm{.}3$ Pilisa takes out a loan to buy a car that costs R$350000.$ The bank offers her an interest rate of $9,3\%$ p$.$a$.$ compounded monthly and a payment period of $6$ years. Her first instalment is due at the end of the first month after taking the loan.

$6\mathrm{.}3\mathrm{.}1$ Calculate Pilisa's monthly instalment.

$6\mathrm{.}3\mathrm{.}2$ Calculate the balance of her loan after the ${40}^{th}$ payment was made.

$6\mathrm{.}3\mathrm{.}3$ Pilisa decides to increase her monthly instalment to R$7000$ per month after her ${40}^{th}$ payment. How long, after the ${40}^{th}$ payment, will it take her to pay up the loan?