10.5.17: First, find an N such that the partial sum s_N(t=5,x=30) is correct up to three decimal places, that is, the following value doesn't change up to three decimal places upon increasing N further:
Using the N you've found, you can find here the x where u(x,t) is maximal for t=5,10,20,40,100,200, and use that to do part (b). You only need to be precise up to integers.
Use the following with the same N to solve part (e). You only need to be precise up to integers.
10.5.18. Second half. The following prints s_N(t=30,x=10) respectively in the silver, aluminium and cast iron cases. Find an N such that the partial sum in the cast iron case is correct up to three decimal places, then record all three values.
10.5.19. The following writes s_N(t,x=10) in the silver, aluminium and cast iron cases respectively. Use the N you've found above to solve the problem. You only need to be precise up to integers.