1 - 3 are fairly straightforward to see how to do.

For the first, simply multiply each component of the matrix by 3.

For the second, calculate 2D and 3B. Now, when you add two matrices, you simply add each component. Ex:

(8 0 -6) = 2D

(6 -6 8)

(9 6 9 )

(12 18 15) = 3B

(8+9 0+6 -6+9)

(6+12 -6+18 8+15) = 2D + 3B

Problem 3 is done the same way.

-Dan