Gigantic cells

Given a new type of cell (spherical shape with radius 5 nm) that lives by absorbing $O_2$ and releasing $CO_2$ . The cell only dies when the intake of $O_2$ is less than releasing of $CO_2$ Given that each $nm^3$ of the cell absorb $O_2$ and release $CO_2$ at the same rate, while each $nm^2$ of the cell membrane can allow the exchange of products from each $15nm^3$ If a scientist enlarge the cell without changing its rate of production and cell wall permeability What is the maximum percentage of volume can he enlarge the cell such that the cell still lives.