electron mobility

Assume that the mobility of electronics in silicon at T=300K is MUn=1300cm^2/V-s.  Also assume that the mobility is limited by latice scattering and varies as T^-(3/2).

Determine electron mobility at (a) T=200K and (b) T=400K.

(There are numerous graphs in the book and no formulas that I could find to help solve this problem.  I tried extrapolating the information from one of the graphs but I couldn't get anywhere.  How do I solve this problem?)