To solve this problem you must apply the proccedure shown below:
1. You have that the arc lengt is 6 and the area os 78,5 cm^2. Therefore, you must apply the following formula:
Arc lenght=radius x θ
2. The value of the radius is:
A=2πr²
r=√A/2π
r=√25
r=5
3. When you clear θ , you obtain:
θ=Arc length/radius
θ=6/5 radians
Therefore, the answer is:6/5 radians