When an object is suspended from a spring balance $($figure $($a$))$ the reading is $5\mathrm{.}40$ N $.$ When the suspended object is submerged in water $($figure $($b$))$ the reading is $3\mathrm{.}90$ N $.$ Determine the density of the object.

$k\frac{g}{m^3}$

$($a$)$