-18 ≤ 4x - 7 ≤ -6 , you are trying to get only x in the middle part
so add 7
-11 ≤ 4x ≤ 1
now divide by 4
-11/4 ≤ x ≤ 1/4
-18 is less than or equal to 4x-7 is less than or equal to -6
(Please explain in detail so I know for the future)
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