Given set of scores= 566, 455, 678, 989, 342, 715

We know the formula,

 $\mathrm{Average} \left(\mathrm{A}\right)=\frac{\mathrm{Sum} \mathrm{of} \mathrm{given} \mathrm{values} \left(\mathrm{S}\right)}{\mathrm{Total} \mathrm{number} \mathrm{of} \mathrm{values} \left(\mathrm{N}\right)}$

 Here,

 Sum of given values(S)

= 566+455+678+989+342+715

= 3745

Total number of values(N)= 6

Substituting these values we get (A),

 $= \frac{3745}{6}=624.16$

Hence, Option C is correct.