capital structure and finance costs

rivision13.8/ 30 June 20×2 a company had $1m 8% loan notes in issue, interest being paid half-yearly on 30 June and 31 December.
on 30 September 20×2 the company redeemed $250,000 of these loan notes at par, paying interes due to that date.
On 1 April 20X3 the company issued $500,000 7% loan notes, interest payable half-yearly 31 March and 30 September.
what figure should appear in the company’s statement of profit or loss for interest payable in the year ended 30 June 20X3?
A $88,750
B $82,500
C $65,000
D $73,750
The answer is D.
July-September (1,000,000× 8% x 3/12)=20,000
October-March (750.000× 8% × 6/12)=30,000
April-June
( 750,000 ×8% × 3/12 )=15,000
(500,000 x 7% x 3/12)=8,750
*Total interest payable in S.P/L=73.750
#anyone explain the answer please ,
# & why we added 500 with 250 ?