Answer:
The expected cost is $8.75
Explanation:
Given

--- If Bob and Anna meet
--- If Bob and Anna do not meet
Required
The expected cost of Bob's meal
First, we list out all possible time both Bob and Anna can select
We have:



The outcome of them meeting at the same time is:


The probability of them meeting at the same time is:



The outcome of them not meeting:


The probability of them meeting at the same time is:



The expected cost is then calculated as:



Take LCM



The expected cost is $8.75