Please help withis matrix

I am really lost with this could anyway show me with working out how to solve

A=(2 1 3)

(1 0-6)

(4 2 7)

B=(3 2 3 )

( 4 6 5)

C=(1 -1 4)

(2 5 -3)

(-3 4 0)

D=(4 0 -3)

( 3-3 4)

E= (3 7)

(1-6)

(0 4)

Evaluate where possible.

1) 3A

2) 2D+3B

3)3A-2C

4)AB

I know it is probably very easy but if I can see the working out I am sure I can understand it.

I think It is done like this

Matrices can be multiplied only where the number of rows=number of columns in any two given matrices. If this is not the case then two matrices cannot be multiplied. e.g. u say evaluate 3A where

A=(2 1 3)

(1 0-6)

(4 2 7)

Just multiply each element of A by 3 hence 3A=(6 3 9)

(3 0 -18)

(12 6 21)