Show that for slightly anisotropic turbulence, the return-to-isotropy can be modeled by a linear Rotta model, and derive the timescale for the anisotropy tensor to decay to zero.
If you are teaching from the book, contact directly. In rare cases, they may provide partial solutions or instructor notes to verified faculty. A First Course In Turbulence Solution Manual
Sites like Physics Stack Exchange are excellent for asking about specific sticking points in Chapter 5 (The Statistical Description) or Chapter 8 (Spectral Dynamics). Final Thoughts Show that for slightly anisotropic turbulence