Use the formula on-screen. r means radius, and π is pi, which the question tells you to approximate as 3.14. The radius is 13cm. The formula is 2πr, so multiply 2 by 3.14 by r. 2 x 3.14 x 13 = 81.64. To round to the nearest tenth, look at the hundredths digit. It is 4, and 4 < 5, so you round down. 81.64 rounded to the nearest tenth is 81.6. Don't forget units.
Answer: 81.6cm