Your answer is 500, review the image I created to understand how I got my answer.
Answer:
The Pythagorean Theorem, a2+b2=c2, a 2 + b 2 = c 2
I dont know the exact positions to put the lengths, but tell me if this helps!
The percent error is 4.167 %
<em><u>Solution:</u></em>
Given that, Mrs Franklin's speedometer said she was driving at a rate of 48 miles per hour
When checking the accuracy of her speedometer, an Automotive Specialist recorded her speed at 50 miles per hour
<em><u>The percent error is given by formula:</u></em>
Percent error is the difference between a measured and known value, divided by the known value, multiplied by 100%

From given,
Experimental value = 50
Theoretical value = 48
<em><u>Substituting the values in formula, we get,</u></em>

Thus the percent error is 4.167 %
I would say no, if you follow the lines on the graph, 12 on the x axis and 5 on the Y axis they are not within the range indicated in gray.