1.
Let A=(2a013105b)A = \begin{pmatrix} 2 & a & 0 \\ 1 & 3 & 1 \\ 0 & 5 & b \end{pmatrix}. If A3=4A2A21IA^{3} = 4A^{2} - A - 21I, where II is the identity matrix of order 3×33 \times 3, then 2a+3b2a + 3b is equal to: