Answer:
 The df values for the A x B interaction are also 3,40 
Step-by-step explanation:
The F-value for Factor A has df = 1, 40 
The F-value for Factor B has df = 3, 40.
 The df values for the A x B interaction are also 3,40 
This is because the source of variation between columns has ( c- 1); rc(n-1) degrees of freedom and  the source of variation between  rows has (r-1); rc(n-1) degrees of freedom and the  source of variation of interaction 
(between rows and columns)  has ( c-1) ( r-1); rc(n-1) degrees of freedom.
Therefore 
Factor A:  ( c- 1); rc(n-1)    = 1,40
<u>Factor B:    (r-1); rc(n-1)     = 3,40</u>
 Interaction : ( c-1) ( r-1); rc(n-1)   =  3*1,(40)= 3,40
where c refers to columns , r refers to rows and n refers to the total sample size.