Evaluating Piecewise Function

Consider the function defined by the piecewise equation:

$$ f(x) = \begin{cases} 2x + 3 & \text{if } x < 1 \\ x^2 - 4 & \text{if } 1 \leq x < 3 \\ 6 - x & \text{if } x \geq 3 \end{cases} $$

Determine the value of $f(2)$ and $f(4)$. Then, calculate the expression $f(2) + f(4) - 5$.