My english is sometimes not good, so I will type from the question I need helping with.

Suppose that  p(t) = [p_0 + p_1 \sin (\omega t]) is the density of oxygen in the wall a < r < b of a spherical cell at time t in an animal whose heart pumps at angular frequency  \omega . Here  p_0, p_1, a, b are positive constants, and  r = \sqrt {x^2 + y^2 + z^2} .

Find Q(t), the amount of oxygen in the cellwall at time t.

Find the most general flux vector of the form  J^{\to} (x,y,z,t) = f(r,t) r^{\to}, \text{where} \ r^{\to} = xi^{\to} + yj^{\to} + zk^{\to} such that p and  J^{\to} satisfy the O2 conservation equation

 \frac{\partial p}{\partial t} + div J^{\to} = 0 .