1. The problem is to find the determinant of the 2x2 matrix $$\begin{pmatrix} 85 & -4 \\ -3 & ? \end{pmatrix}$$. However, the matrix is incomplete as the bottom right element is missing. 2. The determinant of a 2x2 matrix $$\begin{pmatrix} a & b \\ c & d \end{pmatrix}$$ is calculated by the formula: $$\det = ad - bc$$ 3. Since the bottom right element is missing, we cannot compute the determinant without the full matrix. Please provide the complete matrix to proceed with the calculation.