math

At the ruins of Caesarea, archaeologists discovered a huge hydraulic concrete block with a volume of 945 cubic meters. The block's dimensions are x meters high by 12x - 15 meters long by 12x - 21 meters wide. What is the height of the block?
I have no idea how to do this. Can someone please help me?

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  1. remember , volume = lwh

    x(12x-15)(12x-21) = 945
    simplifying a bit

    x(3)(4x - 5)(3)(4x-7) = 945
    x(4x-5)(4x-7) = 105
    16x^3 -48x^2 +35x - 105=0
    by grouping ...
    16x^2(x - 3) + 35(x-3) = 0
    (x-3)(16x^2 + 35) = 0
    x = 3 or x^2 = -35/16 , which is not real

    so the only real solution is x = 3

    so the block is 3 m high,

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  2. How do you get 105?

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  3. I divided both sides by 9
    945÷9=105
    notice the (3)(3) is gone on the left side

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