The difference of twice a number and 4 is at least -27

The difference of twice a number and 4 is at least -27.

The phrase a number means an arbitrary variable, let's call it x.
x

Twice a number means multiply the number by 2
2x

and 4 means we add 4 to our expression:
2x + 4

Is at least means an inequality. In this case, it's greater than or equal to:
2x + 4 >= -27

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