Calculating View Factors for Three Surfaces Using Reciprocity Relation

[princejan7]

Homework Statement

I found the values $F_{3\rightarrow(1+2)}=0.32$ and $F_{1\rightarrow3}=0.25$
I now want to find $F_{2\rightarrow3}$

Homework Equations

Reciprocity relation
$A_iF_{i\rightarrow j}=A_jF_{j\rightarrow i}$

The Attempt at a Solution

Using the reciprocity relation to find $F_{(1+2)\rightarrow3}$
$A_3F_{3\rightarrow(1+2)}=A_{(1+2)}F_{(1+2)\rightarrow3}$
$3(0.32)=6F_{(1+2)\rightarrow3}$
$F_{(1+2)\rightarrow3}=0.16$

Using that to find $F_{2->3}$:
$F_{1\rightarrow3}+F_{2\rightarrow3}=0.16$
$0.25+F_{2\rightarrow3}=0.16$
$F_{2\rightarrow3}=-0.09$

But I get a negative value

 

[haruspex]

$F_{(1+2)\rightarrow3}=0.16$
$F_{1\rightarrow3}+F_{2\rightarrow3}=0.16$

I don't think $F_{(1+2)\rightarrow3}=F_{1\rightarrow3}+F_{2\rightarrow3}$