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In 9 hours (9 = 11-2 hours), they covered 860 - 230 = 630 miles.
Hence, their average speed was 630/9 = 70 miles per hour.
It means that the linear equation relating D and t is D = 1000 - 70t miles. ANSWER
Solved.
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to the author/(the composer) of this problem --- a POST-SOLUTION note.
Actually, having only one piece of info
"After driving a total of 2 hours, they are 860 miles away from their destination"
is just ENOUGH to create such a function and to answer the problem's question.
The other piece of info
"After driving a total of 11 hours, they are 230 miles away from their destination"
is just EXCESSIVE and UNNECASSARY . . .