Two objects, a and b, are held one meter above the horizontal ground. the mass of b is twice as great as the mass of a. if pe is the gravitational potential energy of a relative to the ground, then the gravitational potential energy of b relative to the ground is

Formula for potential energy is:
pe = m * g * h
Where:
m = mass of an object
g = gravitational acceleration
h = height at which object is placed

From this equation we can make conclusion that increasing mass also increases potential energy. Object b has double the mass so it has double the potential energy.
Object a:
pe = m * 9.81 * 1
pe = 9.81 J
Object b:
pe = 2m * 9.81 * 1
pe = 19.62 J