The recurrence relation to count number of function call looks like,
$F(a,b)=1+F(min(a,b),min(a,b))+F(max(a,b)-min(a,b),min(a,b))$ if $a\neq b$
=1 if $a= b$
$F(3,12)=F(3,3)+F(9,3)+1$
$F(9,3)=F(3,3)+F(6,3)+1$
$F(6,3)=F(3,3)+F(3,3)+1$
now ,$F(3,3)=1$ as a=b
putting the value in $F(6,3)$ we get ,
$F(6,3)=3$
$F(9,3)=5$
$F(3,12)=7$
so correct answer is 7.