= Solution
For a constant orthogonal Cartesian change of coordinates $x'_i=Q_{ij}x_j$, the <tensor component transformation law> for order $n$ is
$$
\boxed{T'_{i_1\cdots i_n}=Q_{i_1j_1}\cdots Q_{i_nj_n}T_{j_1\cdots j_n}.}
$$
Repeated indices are summed. In Cartesian orthonormal coordinates the metric identifies upper and lower indices, so the same orthogonal matrix acts on every index.
An <isotropic tensor> has the same numerical components after every proper orthogonal change of axes: $Q^{\otimes n}T=T$ for every $Q$ with $Q^TQ=I$ and $\det Q=1$. For example, $\delta_{ij}$ is isotropic because $Q_{ik}Q_{jk}=\delta_{ij}$. Some conventions require invariance under all orthogonal transformations, including reflections; this stronger convention must be distinguished for odd-order tensors, notably the <Levi-Civita symbol>, which is invariant under proper rotations but changes sign under its ordinary three-index transformation for a reflection.
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