Solve for x. 13 x 18 8

Nevermind, I see it.

Solve for all parts.

Simultaneous

Not the complete answer

Cutting Timber. A stand of fir trees occupies 60 acres, with an average density of 200 trees per 20 acres. A forester estimates that each tree will yield 400 board-feet of lumber. Estimate the yield of the stand in board-feet if one-tenth of the trees are cut.

Solution

I need answers and explanation

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need the answer