The surface of a solid sphere is covered by a monolayer of receptors for a ligand. When the ligands diffuse to the surface of the sphere, they are captured instantaneously by the receptors. The ligand diffusion coefficient is 1.7*10-9m2/s. Assume the bulk concentration far away from the sphere is constant of 2.5 nM and the sphere radius is 3.1 μm. Find the total ligand flux onto the surface of the sphere. The answer is in the form of A*10-18 mole/s. Please enter the value of A in the box.