\[\boxed{\mathbf{394}.}\]
\[P(x) = Q_{1}(x)(x + 2) +\]
\[+ 6 \rightarrow P( - 2) = 6.\]
\[P(x) = Q_{2}(x)(x - 3) +\]
\[+ 26 \rightarrow P(3) = 26.\]
\[P(x) = Q_{3}(x)(x + 4) +\]
\[+ 12 \rightarrow P( - 4) = 12.\]
\[7a = 7\]
\[a = 1.\]
\[b = 4 - a = 4 - 1 = 3.\]
\[c = 6 - 4 \cdot 1 + 2 \cdot 3 = 8.\]
\[Ответ:R = x^{2} + 3x + 8.\]