Answer:
C.A 30 kg suitcase at a height of 2 m 
Explanation:
The gravitational potential energy (GPE) of an object is given by:
[tex]U=mgh[/tex]
where
m is the mass
g is the gravitational acceleration
h is the heigth above the ground
We can use the formula to calculate the GPE of each object:
A.A 30 kg suitcase at a height of 1.5 m
[tex]U=(30 kg)(9.8 m/s^2)(1.5 m)=441 J[/tex]
B.A 20 kg suitcase at a height of 2 m
[tex]U=(20 kg)(9.8 m/s^2)(2 m)=392 J[/tex]
C.A 30 kg suitcase at a height of 2 m 
[tex]U=(30 kg)(9.8 m/s^2)(2 m)=588 J[/tex]
D.A 20 kg suitcase at a height of 1.5 m.
[tex]U=(20 kg)(9.8 m/s^2)(1.5 m)=294 J[/tex]
So, we see that the object which has the most GPE is C.