We propose iterative inversion algorithms for weighted Radon transforms $R_W$ along hyperplanes in $R^3$. More precisely, expanding the weight $W = W (x, \theta), x \in R^3 , \theta \in S^2$ , into the series of spherical harmonics in $\theta$ and assuming that the zero order term $w_{0,0}(x)$ is not zero at any $x \in R^3$ , we reduce the inversion of $R_W$ to solving a linear integral equation. In addition, under the assumption that the even part of $W$ in $\theta$ (i.e., $1/2(W (x, \theta) + W (x, −\theta))$) is close to $w_{0,0}$, the aforementioned linear integral equation can be solved by the method of successive approximations. Approximate inversions of $R_W$ are also given. Our results can be considered as an extension to 3D of two-dimensional results of Kunyansky (1992), Novikov (2014), Guillement, Novikov (2014). In our studies we are motivated, in particular, by problems of emission tomographies in 3D. In addition, we generalize our results to the case of dimension $n > 3$.