Answer
$27.4 \frac{m}{s^2}$
Work Step by Step
Equation 5-5 gives g, the acceleration due to gravity near the surface of Earth. If the mass of Earth were to increase by 2.80, other things being equal, g would increase by the same factor.
$$(2.80)(9.80 \frac{m}{s^2}) = 27.4 \frac{m}{s^2}$$