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!