I would say -100
You would find this out by identifying your 'a' which is the first number of the sequence, in this case it is -5
Then you would find the common ratio. You do that by dividing any two of the numbers after your 'a' For this one I chose to divide -20 by -10 and that gets you 2.
You would multiply those together, getting you -10.
So, from here you would put the term you are trying to find (in this case it is the 11th term) and subtract it by one
11-1=10
Lastly, you would multiply your -10 by 10 and get yourself a -100
Formula: nth term = a1^n-1
Hope this helps :) Sorry if it is kinda confusing...