To find the sum of the two vectors, we simply need to add the corresponding components of the vectors together.
So if we have vectors \( \mathbf{a} = \begin{bmatrix} a_1 \\ a_2 \end{bmatrix} \) and \( \mathbf{b} = \begin{bmatrix} b_1 \\ b_2 \end{bmatrix} \), their sum \( \mathbf{c} = \mathbf{a} + \mathbf{b} \) would have components \( c_1 = a_1 + b_1 \) and \( c_2 = a_2 + b_2 \). Specifically, for the given vectors: \( \mathbf{a} = \begin{bmatrix} 4 \\ -5 \end{bmatrix} \) and \( \mathbf{b} = \begin{bmatrix} 10 \\ 2 \end{bmatrix} \), we have \( \mathbf{a} + \mathbf{b} = \begin{bmatrix} 4 + 10 \\ -5 + 2 \end{bmatrix} = \begin{bmatrix} 14 \\ -3 \end{bmatrix} \).
Therefore, the sum of the vectors is: \( \mathbf{c} = \begin{bmatrix} 14 \\ -3 \end{bmatrix} \), which corresponds to option b.