On day no 9, because to increase her mileage by 4 to reach 8 it will take her 4/0.5=8 days plus day 1 where she ran just 4 miles.
Answer:
x= 10
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21 cars, 32 motorcycles.create a system of equations using x for cars and y for motorcycles.

multiply the top equation by 2 to prepare for elimination method

subtract terms

divide both sides by negative 2 to solve for x
x =21
plug in x into original equation to solve for y.
21 + y = 53
subtract both sides by 21
y=32