Using a calculator, find the radius of the circular arc if the arc contains 138 degrees and its length is 15 cm.

1) Let the required radius be R. Then the length of the whole circle is equal to 2πR.
2) The whole circle corresponds to an arc of 360 °, and we have an arc of 138 °. Then the length of our arc is calculated using the following formula: l = (138/360) * 2πR = (23/60) * 2πR = 23πR / 30.
3) By the condition l = 15 cm. Then we have an equation from which R can be found: 23πR / 30 = 15.
4) We get that R = 450 / 23π. The number is π ≈ 3.14. Let’s calculate R using a calculator and get R ≈ 6.23 cm.
ANSWER: 6.23 cm.