$5($a$).$ A solid ball has a weight of $3\mathrm{.}5$ N $.$ When it is submerged in water $($density of water is $1,000k\frac{g}{m^3}),$ it has an apparent weight is $2\mathrm{.}7$ N $.$ What is the density of the ball?

$($b$).$ The water in the plumbing in a house is at a gauge pressure of $190,000Pa.$ What force does this gauge pressure cause on the top of the tank inside a water heater if the area of the top is $0\mathrm{.}7m^2?$