Acircle has a radius of 12.6 cm. what is the exact length of an arc formed by a central angle measuring 120°? enter your answer in the box. express your answer using π .

We know that

[the length of a circumference]=2*pi*r
for r=12.6 cm
[the length of a circumference]=2*pi*(12.6)> 25.2*pi cm
this is the length for an arc of 360°  (full circumference)

now calculate the length for an arc of 120° (applying a rule of three)  
if 360°> 25.2*pi cm
 120°> X
X=120*25.2*pi/360> 8.4*pi

the answer is 8.4*pi