The increase in gravitational potential energy for an object of mass m is given by
[tex]\Delta U = mg \Delta h[/tex]
where [tex]\Delta h[/tex] is the increase in altitude of the object.
In our problem, m=3.0 kg, [tex]\Delta h= 2.6 m[/tex] and [tex]g=10 m/s^2[/tex] (approximated value), so we have
[tex]\Delta U = mg\Delta h=(3.0 kg)(10 m/s^2)(2.6 m)=78 J[/tex]
