tolong dibantu jawab :p

4. 3b+1p = 9000 ×2 | 6b+2p =18000
2b+2p= 8400 ×1 | 2b+2p = 8400
____________ -
4b = 9600
B = 2400
3(2400)+1p = 9000
P= 9000-7200
= 1800
P= pensil
b= buku