Let "per month" = m
The inequality is
1.5m + 4 ≥ 7
+ 4: Her hair right now is 4 cm long
1.5m: Her hair grows 1.5 per month (m)
≥ 7: She wants it to be at least 7 or more.
1.5m + 4 ≥ 7 is your answer
hope this helps
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