Solve the design problem

I need the answer in another 30 mins...budget max 6 dollar A silica multimode step-index fiber has core and cladding refractive indices of 1.48 and 1.46, respectively. The equilibrium length of the fiber is 2 km. The light source emits at 820 nm and has a spectral width of 120nm. Compute the electrical 3-dB bandwidth of a 5-km length of this fiber and the maximum RZ and NRZ data rates. Repeat the problem for a Graded-index fiber when the spectral width of the light source is reduced to 20 nm.