Give a big-o estimate for the number additions used in this segment of an algorithmi: =0 , for i: =1 to n, for j: = 1 to n, t: =t+i+j

We have a "square" double loop, meaning that both loops go to completion at n.
So there are n^2 executions of t:=t+i+j.
Assuming two additions per execution of the innermost loop, (i.e. ignoring the implied additions in increment of subscripts), we have 2n^2 additions in all.

Therefore the given code section is of O(n^2), i.e. the highest power (if polynomial) and ignore coefficients.

Just turn the whole gym into pie