A copper crystal emits 8.3 x 1010 photoelectrons/m2 s. ?

From density and at. wt. you can compute no. of atoms/m^3 Na and the cube root of Na is the lattice linear density in atoms/m. Now calculate the no. of atoms in 5 layers 1 m^2 in area. Divide by 8.3E10 e/m^2 and you have how many atoms it takes on average to provide 1 e/s. (Which I ume the somewhat ambiguously worded question asks for. The other interpretation has 8.3E10 as the answer.)