If x denotes the value of the area then your answer (360° x = 115° $\displaystyle \pi$ 4² )gives the value of the non-shaded area.
Oh so im wrong . all i did here was 115 over 360 and then sector area which is x over area of circle which is 4cm^3*pi and cross multiplied sorry I couldnt give the result to that in this post im going to school atm