If `x\ a n d\ y` vary inversely as each other and `(i) x=3\ ` when`\ y=8,\ ` find`\ y\ ` when`\ x=4` `(ii) x=5\ ` when`\ y=15 ,\ ` find`\ x\ ` when`\ y=12` `(iii) x=3,\ ` find`\ y\ ` when constant of variation`=900.` `(iv) y=35 ,\ ` find`\ x` when constant of variation`\ =7.`