\[y = - x^{2} + 4x + 3;\ \ \ \lbrack 0;5\rbrack.\]
\[m = - \frac{b}{2a} = - \frac{4}{- 2a} = 2;\ \ \]
\[n(2) = - 4 + 8 + 3 = 7.\]
\[y(0) = 3;\]
\[y(5) = - 25 + 20 + 3 = - 2.\]
\[E(y) = \lbrack - 2;7\rbrack.\]