If Mass of the sphere is M, Mass of the carved out sphere is MR3×(R2)3=M8
Consider the larger sphere to be made of positive mass M and negative mass −M8
Net force on the +M8 sphere is
GMM8(3R)2+G(−M8)(M8)(3R−R2)2=GM2R2(172−1400)=GM2R2(50−9400)=41GM23600R2