A semi$-$elliptical leaf spring $900$ mm long and $55$ mm wide is supported at the centre by a $50$ mm wide band. If the thickness of each leaf is $5$ mm$,$ find the number of leaves required to support a load of $4500$ N$.$ Assume a maximum working stress of $490$ MPa. If two such leaves extend the full length of the spring, find the deflection of the spring. The Young's modulus for the spring material can be taken as $210$ kN$/$mm$2.$