Two coils are made from two wires of same length. If their radii ratio is 3:4  then their no of turns  ratio is 

If same length of the wire is used to make a coil then length of the wire l =$2\pi nr$ is constant.

$2{\mathrm{\pi r}}_1{\mathrm{n}}_1=2{\mathrm{\pi r}}_2{\mathrm{n}}_2$

$\frac{{\mathrm{n}}_1}{{\mathrm{n}}_2}=\frac{{\mathrm{r}}_2}{{\mathrm{r}}_1}=\frac{4}{3}$