How to add limited row to specific row

Hello all I'm student I'll be glad to help me to solve below problem, that I've two matrices A is 2x9 and B is 6x3,

A= zeros(2,9)

A =

   0     0     0     0     0     0     0     0     0
   0     0     0     0     0     0     0     0     0
  B=round(10*rand(6,3))

B =

   7     6     9
   6     7     8
   4     1     7
   1     1     1
   8     5     1
   3     5     1

by using these codes I want to add first three row of matrix B to first row of A and second three rows of matrix B to second row of matrix A by using these codes :::

for i=1:6

        if i<=3     

            x=x(y,:)
        else 

       end           
    end

I tried I don't know how inside if condition

Answer 1

[Andrei Bobrov]

A= zeros(2,9);
B = [7     6     9
   6     7     8
   4     1     7
   1     1     1
   8     5     1
   3     5     1];

out = reshape(B',fliplr(size(A)))'

Answer 2

[Azzi Abdelmalek]

A= zeros(2,9)
B=round(10*rand(6,3))
d=B'
out=[A reshape(d(:),9,[])']

[hewaa mero]

but is will give some zero coloms before adding in the new matrix

[Azzi Abdelmalek]

You said add not replace

[hewaa mero]

your right i mean replace thanks for your feedback

Answer 3

[dpb]

Don't need any if (if I understand your request, anyway)...

>> A = reshape(B',9,[])';
A =
   7     6     9     6     7     8     4     1     7
   1     1     1     8     5     1     3     5     1
>>

ADDENDUM:

Which is the same as Andrei's identically if one doesn't recognize the "9,[]" as equivalent to fliplr(size(A))