The absolute value of a number returns the positive value of the given number. Ruben will be at exactly 90 miles in 2 hours or 5 hours
Given that:
[tex]d = |210 - 60t|[/tex]
To calculate t when [tex]d = 90[/tex], we have:
[tex]90 = |210 - 60t|[/tex]
Rewrite as:
[tex]|210 - 60t| = 90[/tex]
Remove absolute bracket
[tex]210 - 60t = 90 \ or\ 210 - 60t = -90[/tex]
Collect like terms
[tex]- 60t = -210 + 90 \ or\ - 60t = -210 -90[/tex]
[tex]- 60t = -120 \ or\ - 60t = -300[/tex]
Divide through by -60
[tex]t = 2 \ or\ t = 5[/tex]
Hence, Ruben will be at exactly 90 miles in 2 hours or 5 hours
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