Statistics expectation q

This is the link to the question, it's question 4ii:

http://www.mei.org.uk/files/papers/s108ja_leqa.pdf

I found the expectation in the first part of the q to be 2.952. The question says it costs £45,000 to investigate each site and to find the total cost. I can see from the table there's 4 sites and the expectation formula is E = n x p so why can't the answer be E = 4 x 0.2 as it says the probability of finding oil is 0.2?

The answer is actually 2.952 x £45,000 but I don't understand why. What information did the expectation even give me?

Thanks

The expectation is the expected number of sites checked.

So does the table's r values basically just show if they visited those sites, those would be the probabilities but they only actually visited 2.952 sites?