First, let's calculate the actual cost.

is the actual cost of six nights.
The formula for percent error is
The bars (|) stand for absolute value which gets rid of the negative sign if there is one.
Plug in the values:

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<span> is the percent error.</span>
-0.8 mhm :)
how: u add them all up n then divide by how many numbers there are !! in this case: 2+2+-2+-4+-3+0 = -5 and there’s 6 numbers and then 5/6 is .83 repeated but u just round to .8 because, “four or less, give it a rest ... five or more raise the score!” that’s how i remember :) i already saw an answer for this but i decided to explain anyways in case u didn’t understand. have a great day<3