note the equation/formula:
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d * r = t ;
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in which:
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d = distance = 84 ft.
r = rate = 12 ft / sec
t = time = ?
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To find the "time" we can rearrange the equation:
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d = r * t ;
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Divide EACH SIDE of the equation by "r" ; to isolation "t" on one side of the equation; to create an expression to find the time for the given distance and rate; which we will then do by plugging in our given values for "d" (distance) and "r" (rate) ;
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d / r = (r * t) / r ;
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to get : d / r = t ;
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↔ t = d / r ;
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Now, plug in our given values for "d" and "r" ; to solve for "t" ;
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→ t = 84 ft / (12 ft / sec) ;
= 84 ft ÷ ;
= 84 ft * ;
= { } sec. ;
→ t = 7 sec. {that is; "7 seconds" }