Suppose the cells of a tumor are idealized as spheres each with a radius of 5 muμm (micrometers). the number of cells has a doubling time of 35 days. approximately how long will it take a single cell to grow into a multi-celled spherical tumor with a volume of 0.8 cm^3 (1 cm=10,000 μm)? assume that the tumor spheres are tightly packed.