Using proportions, it is found that:
a) The expression describes the situation because for each day late, she loses $5, hence for 4 days she loses 4 x (-5) = -$20.
b) The expression is: -5x.
A proportion is a fraction of a total amount, and the measures are related using a rule of three. Due to this, relations between variables, either direct or inverse proportional, can be built to find the desired measures in the problem.
In this problem, we have that for each day late, she has to pay $5, hence the amount she loss after n days is:
L(n) = -5n.
For 4 days, the amount lost is:
L(4) = -5 x 4 = -20.
More can be learned about proportions at https://brainly.com/question/24372153
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