CONSTANTS

An easy way to use constants.
Here is a new function : Cst()

Try this :
[G,g]=Cst([9,8])
r=6.378*10^6
Solve(G*m1*mass/r^2=m1*g,mass)
or
[G,g]=Cst([9,8],1)
r=6.378*10^6_m
Solve(G*m1*mass/r^2=m1*g,mass)