Sphere sits at bottom of milk container, find mass?

[tigers4]

Homework Statement

A glass ball of radius 2.40 cm sits at the bottom of a container of milk that has a density of 1.03 g/cm3. The normal force on the ball from the container's lower surface has magnitude 7.50 *10^-2 N. What is the mass of the ball?

Homework Equations

F_b=M_f*g
d=M/V
4/3pir^3=V

The Attempt at a Solution

F_b+(7.5*10^-2)=M_ball*g
but it says I am wrong

 

[gneill]

They are probably looking for a numeric solution.

The given normal force should be equal in magnitude to 'net weight' of the glass ball in the fluid, which in turn will equal the force due to gravity on the ball less the buoyant force.