A payment of R$100000$ due in $25$ years time is purchased from a company by means of level monthly payments. $5\%$ of each payment is taken by the company as expenses.

Interest is calculated at $12\%$ p$.$a$.$ compounded quarterly. Find the monthly payments if:

$($a$)$ Payments begin immediately and stop in $20$ years time.

$($b$)$ Payments begin in six months time and cease in $24$ years time.

$($c$)$ Payments begin in five years time and cease one month before the payment of R$100000.$