ANSWER
[tex]3 \: radians[/tex]
EXPLANATION
The formula for the calculating the length of an arc is
[tex]l = r \theta[/tex]
where theta is in radians.
From the diagram
[tex]l = 12cm[/tex]
[tex]r = 4cm[/tex]
We substitute the values to obtain;
[tex]4\theta = 12[/tex]
Divide both sides by 4 to get;
[tex]\theta = \frac{12}{4} [/tex]
[tex]\theta = 3 \: radians[/tex]
