Weighted average capitalisation rate

Hello Sir,

In Kaplan attempt to answer the following question of capitalised cost of borrowing in the this way

Weighted average capitalisation rate =
(9% × 15 / 39) + (11% × 24 / 39) = 3.5% + 6.8% = 10.3%
$
Borrowing costs =
$6m × 10.3% × 9/12 463,500
+ $2m × 10.3% × 5/12 85,833
= 549,333

But according to the lectures seems to be more logical was as in this way

15 X 9% = $1.35
24 x 11%= $ 2.64
total = $ 3.99

then ($3.99 / 39)x100 = 10.23%

$6mx10.23%x9/12 = $ 460350
$2mx10.23%x5/12 = $ 85250

total interest = $ 545600

So by this way we will have slight difference than the kaplan way because of the difference in
the weighted average capitalisation rate

which way we have to use?

Thanks,

Carriageways Co had the following bank loans outstanding during the whole of 20X8 which form the
company’s general borrowings for the year:
$m
9% loan repayable 20X9 15
11% loan repayable 20Y2 24
Carriageways Co began construction of a qualifying asset on 1 April 20X8 and withdrew funds of $6 million
on that date to fund construction. On 1 August 20X8 an additional $2 million was withdrawn for the same
purpose.
Calculate the borrowing costs which can be capitalised in respect of this project for the year ended
31 December 20X8.
A $549,333
B $411,999
C $750,000
D $350,000