Answer :

[tex]9=7d+8(9-2d)\\9=7d+72-16d\\9=-9d+72\\-72+9=-9d\\-63=-9d\\d=7[/tex]

Also for the 8(9-2d), simplify by multiplying the 8 into the (9-2d) as we get (8*9)-(8*2d) = 72-16d

Therefore, the answer is d = 7 aka C.

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