Question 291156
I'm assuming that the formula given to you is {{{t=sqrt(d/16)}}}



a) 


{{{t=sqrt(d/16)}}} Start with the given equation.



{{{t=sqrt(64/16)}}} Plug in {{{d=64}}}



{{{t=sqrt(4)}}} Divide 64 into 16 to get 4.



{{{t=2}}} Take the square root of 4 to get 2.



So it takes 2 seconds for an object to fall 64 ft.


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b) 


{{{t=sqrt(d/16)}}} Start with the given equation.



{{{9=sqrt(d/16)}}} Plug in {{{t=9}}}



{{{9^2=d/16}}} Square both sides to eliminate the square root.



{{{81=d/16}}} Square 9 to get 81.



{{{81*16=d}}} Multiply both sides by 16 to isolate 'd'



{{{1296=d}}} Multiply



So the answer is {{{d=1296}}} which means that the object has fallen 1,296 ft in 9 seconds.