Please, any help with this problem on Z trabsforms:

A man's assets in connection with time k (in years) are c(k) and his expenses are e(k). They both satisfy the diff. equations c(k+1)=1,5c(k)-e(k) and e(k+1)=0,21c(k)+0,5e(k).

a. Find the % increasement of the assets per year

b. If the initial assets are 6000 Euro and the expenses during the first year are 3720 Euro, find the year whose expenses are least as well as the assets at that year's beginning.

THANK YOU VERY MUCH!