Answer:
12
Step-by-step explanation:
The cost for n attendees will be ...
cost = 2 + 2n
We want the cost to be, at most, 26, so we have ...
26 ≥ 2 +2n
Dividing by 2 gives ...
13 ≥ 1 + n
And subtracting 1, we find the answer:
12 ≥ n
At most, there can be 12 attendees.