book Maths Puzzle Numerical Ability

Fill in the blanks:

_ _ - ( _ / _ ) =9

the only numbers you can use are 3, 4, 6, 8, and 9

the same goes for this problem:

_ _ / _ + _ _ = 418

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book Other Question

I get this far and then stuck and not sure if its right.

Simply and write answer in positive exponents only

(x^2)^-3 (x^-2) divided by (x^2)^4

My answer
x^-1 times x^-
The period of a simple pendulum is directly proportional to the
square root of its length. If a pendulum has a length of 6 feet and a
period of 2 seconds, to what length should it be shortened to achieve
a 1 second period?