Projection constants of the space $l_\infty^{3m}$

The paper considers minimal projections of the space $l_\infty^{3m}$ on some subspace of codimension $m$. Relative projection constants are found for them, and in the case of a minimal projection with a unit norm, the maximum value of the strong uniqueness constant is found. The projection constants found can be used in computational mathematics, in particular, to assess the convergence of projection methods for solving operator equations.