$$
   {\rm Work\ } = F d 
$$

$$
  {F_g}  =  m g
$$

$$
  {F_g} = {{G M_1 M_2} \over{r^2}} 
$$

$$
  {F_g} = {{G \thinspace M_E \thinspace m} \over{{R_E}^2}} 
$$

$$
  {G} = {{F_g \thinspace r^2 } \over {M_1 M_2} } 
$$

$$
  {g} =  {{G M_E} \over {{R_E}^2}} 
$$

$$
  {M_E} =  {{g \thinspace {R_E}^2} \over {G}} 
$$



$$
  {\rm Work \ } = { \int_{R_1}^{R_2}  {{G M_1 M_2} \over{r^2}}  dr }
$$


$$
   {\rm Work\ } =  {\int{ F \thinspace dx } } 
$$


$$
   {\rm Work\ } =  {\int{ \vec{F} \cdot \vec{dx} } } 
$$


\bye
