We give Macaulay2 algorithms for computing mixed multiplicities of ideals in a polynomial ring. This enables us to find mixed volumes of lattice polytopes and sectional Milnor numbers of a hypersurface with an isolated singularity. The algorithms use the defining equations of the multi-Rees algebra of ideals. We achieve this by generalizing a recent result of David A. Cox, Kuei-Nuan Lin, and Gabriel Sosa in. One can also use a Macaulay2 command `reesIdeal to calculate the defining equations of the Rees algebra. We compare the computation time of our scripts with the scripts already available.