Verified answer

7 - 3|4d - 7| ≥ 4

There are two cases.

1) 4d - 7 >= 0. Then the problem is 7 - 12d + 21 >= 4

Add 12d to both sides of the inequality: 28 >= 12d + 4

24 >= 12d

So in case 1, if 4d - 7 >= 0, d <= 2

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Case 2) 4d - 7 < 0, then |4d - 7| = 7 - 4d..............So the equation becomes:

7 + 12d - 21 >= 4

-14 + 12d >= 4

12d >= 18

d >= (3/2)................Which fits 4d - 7 < 0

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3/2 <= d <= 2 <----------- Answer

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