bantuin dong plisss...

3. untung = 20/100 × 75000
= 15000
penjualan = 75000 + 15000 = 90000
per buku = 90000 / 50
= 1800 rupiah.

4. rugi = 20/100 × 60000
= 12000
pembelian = 60000 - 12000
= 48000 rupiah

5. = 750000× 9/12 × 20/100
= 112500 (bunga)
total = 750000 + 112500
= 862500 rupiah

semoga membantu..
(maaf 1 dan 2 tdk bisa)