Request help for these homework questions.

Question $2$

Brian Bell & Co$.$ is selling micro$-$oven for K$4000$ by cash. If this item is purchased on an installments basis where the method of repayment is to deposit K$500$ followed by equal semi$-$annually repayments of K$900$ for three years.

$($a$)$ Calculate the flat rate of interest charged if this item is bought on an installments basis.

$($b$)$ Calculate the total amount paid at the end of $3$ years if this item is bought on installments

basis.

Question $3$

$($a$)$ At the end of each month we plan to invest K$200$ into an account that bears interest compounded monthly. For the first year the interest rate is $8\%$ p$.$a$.$ For the next year it is $7\%$ p$.$a$.$ For the third year it is $6\mathrm{.}5\%$ p$.$a$.$ How much is in the account after $3$ years?

$($b$)$ At the end of every even month we invest K$175$ into an account that bears interest of $11\%$ p$.$a$.$ compounded monthly. At the end of every even month we invest K$155.$ How much will be in the account at the end of $3$ years?