Exam Question - end-to-end delay from video capture to video playout
There are a few mistakes in your math.  

First, you are multiplying an entire group of pictures (7 frames) by 25, that would be 7 seconds of video, not one.  

Second, you are not considering that the first I frame of one set is the last of the next, so it should be assumed that the sequence that would be used is IBBPBBIBBPBBIBBPBBIBBPBB...  It would make no sense at all to put two I frames together in a row, but sometimes the I is listed as an end.  

Third, you are not considering the fact that a B frame is bi-directional and can not be processed until the next I or P frame is reached.

These three things significantly complicate the problem from the simple state you initially thought it was, though as this is an academic problem, I will leave the actual solving as an exercise for you.