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

Suppose that $\displaystyle 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 $\displaystyle \omega $. Here $\displaystyle p_0, p_1, a, b $ are positive constants, and $\displaystyle 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 $\displaystyle 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 $\displaystyle J^{\to} $ satisfy the O2 conservation equation

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