Group of order $1575$ having a normal sylow $3$ subgroup is abelian.
Hint: Pull back Sylow subgroups of $G/P_3$, which are normal, and use the fact that if a Sylow subgroup is normal then it is characteristic.
Hint: Pull back Sylow subgroups of $G/P_3$, which are normal, and use the fact that if a Sylow subgroup is normal then it is characteristic.