Answer:
7 times
Explanation:
So since it rings every half hour, there should be 2 rings every hour, if not you are not on our planet. (60 mins in an hour, 30 mins = 1, so 60 mins =2)
So since it rings for 3 full hours, we get an initial step of 3 * 2 = 6 rings
Then there is another 1/2 ring because 3 and a 1/2 hours. So 6+1=7
hope i helped :) im not sure what you mean by model :(