12÷2=6
6x3= 18
12 pens = 18 pencils
10 pencils and 12 pens = 10+ 18=28 pencils ***55 yuan.
Then each pencil is 55÷28=55/28 yuan ≈ 1.96 yuan.
10 pencil is 55/28x 10=550/28 yuan.
Each pen is (55-550/28)÷ 12≈2.95 yuan.
It's hard to calculate. If it's 56 yuan, it's fine.
56 ÷ 28 per pencil = 2 yuan.
10 pencil is 2x 10=20 yuan.
Each pen is (56-20)÷ 12=3 yuan.
I hope I can help you!