If fourth term of a G.P. is 3, the product of the first seven terms is

63. As the number of terms are odd (7)  let $r$ , be the common ratio 
So terms can be taken as  $\frac{a}{r^3},\frac{a}{r^2},\frac{a}{r},a,ar,a{r}^2,a{r}^3$
$\therefore$   Product  of the term  $=a^7$
$=3^7$ as ($t_4=a=3$ )