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What is the effect on the graph of the function f(x)=x when f(x) is replaced with -f(x)+4

Ineed here’s a picture of the question

Traffic on saturday, it took ms. torres 24 minutes to drive 20 miles from her home to her office. during friday's rush hour, it took 75 minutes to drive the same distance. a. what was ms. torres's average speed in miles per hour on saturday? b. what was her average speed in miles per hour on friday?