Find the gravitational potential at the Earth's surface and at a height of 1.5R above it…

Step 1. Surface. $V = -gR = -6.27 \times 10^{7}\ \text{J/kg}$.

Step 2. Height $1.5R$. $r = 2.5R$: $V = -\dfrac{gR}{2.5} = -2.51 \times 10^{7}\ \text{J/kg}$.

Step 3. Work. $3.0\ \text{kg} \times (6.27 - 2.51) \times 10^{7}\ \text{J/kg} = 1.13 \times 10^{8}\ \text{J}$.