Verified answer

Apply the Mean Value Theorem to f on [4, 7]:

[f(7) - f(4)]/(7 - 4) = f '(c) for some c in (4, 7).

However, f '(c) ≥ 1 by hypothesis.

So, [f(7) - f(4)]/(7 - 4) ≥ 1

==> [f(7) - 2]/3 ≥ 1

==> f(7) ≥ 5.

Hence, f(7) is at least 5.

I hope this helps!