Consider the following 2 × 2 matrix A where two elements are unknown and are marked by a and b. The eigen values of this matrix are -1 and 7. What are the values of a and b?
\[{\text{A}} = \left( {\begin{array}{*{20}{c}} 1&4 \\ {\text{b}}&{\text{a}} \end{array}} \right)\]

A. a = 6, b = 4

B. a = 4, b = 6

C. a = 3, b = 5

D. a = 5, b = 3

Answer: Option D