mainly need part $($b$)$

I am not sure in $($a$)$ I should use mac dur or convexity to estimate, can you tell me which formula I should use?

Problem $2($Required$,25$ marks$)$

The following table shows the market information of the $3$ coupons bonds in the market

The term structure is flat and the annual effective interest rate is $i_0=3\mathrm{.}2\%$ We consider a

bond portfolio containing $1$ unit of Bond A$,1$ units of Bond B and $3$ unit of Bond C$.$

$($a$)$ Using the given information, estimate the value of the bond portfolio if the interest

rate is raised to $4\mathrm{.}6\%.$

$($b$)$ Suppose that the investor invests his capital into this bond portfolio for $5$ years and

the interest rate becomes $4\%$ in coming $5$ years, estimate the IRR of this investment.The following table shows the market information of the $3$ coupons bonds in the market

Current Price Macaulay Duration Modified Convexity

Bond A $93\mathrm{.}263\mathrm{.}1911\mathrm{.}77$

Bond B $108\mathrm{.}046\mathrm{.}1944\mathrm{.}57$

Bond C $105\mathrm{.}918\mathrm{.}5283\mathrm{.}11$

The term structure is flat and the annual effective interest rate is $0=3\mathrm{.}2\%$ We consider a

bond portfolio containing $1$ unit of Bond A$,1$ units of Bond B and $3$ unit of Bond C$.$

$($a$)$ Using the given information, estimate the value of the bond portfolio if the interest

rate is raised to $4\mathrm{.}6\%.$

$($b$)$ Suppose that the investor invests his capital into this bond portfolio for $5$ years and

the interest rate becomes $4\%$ in coming $5$ years, estimate the IRR of this investment.