7,8 tolong pakai caranya

7.
harga beli = 100%
untung  = 15% = Rp 450.,000
harga beli = 100/15 x Rp. 450.000 = 3.000.000

8.
tabungan awal = 100%
bunga 8bulan = 8/12 x 21 % = 14%
tab sekarang = 114% =  456.000
tab awal = 100/114 x 456.000 = Rp. 400.000