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The length of the stalactite that grows for [tex]7.5*10^4[/tex] years is 375 inch.
Explanation
Stalactites can grow at the rate of about 0.005 inch per year.
So, for finding the length that grows for [tex]7.5*10^4[/tex] years, we will just multiply the 'rate of growth' by the 'total time in years'.
Thus.....
[tex]0.005(7.5*10^4)\\ \\ =0.005(7.5*10000)\\ \\ =0.005(75000)\\ \\ =375[/tex]
So, the length of the stalactite that grows for [tex]7.5*10^4[/tex] years is 375 inch.