Q1. Drug transport in tumor could be modeled by tumor spheroid model a.Derive an equation for u (drug concentration) in terms of r (tumor spheroid radius) b. Calculate the critical radius at which necrosis will occur c. Find u, when drug diffuses until half the size of the radius. Assume the maximum spheroid radius as b; the concentration of drug at the surface as ub. When r=a,U(a)=0.b>2a