you'll make calculations (and life) much easier for yourself if you use the "store" capability of the graphing calculator.

to store a value ...

1. type out the value

2. hit the[STO]button

3. hit the[ALPHA]button and select the letter you want to store the value into.

4. press[ENTER]to store the value

for example, to store the universal gravitational constant, your screen will display ...

6.673E-11 -> Ghit

[ENTER]and it's done.

store the mass of the planet in M ...

6.392E23 -> M

[ENTER]

add the planet radius and the height and store in R ...

(did you remember to change km to m for h?)

3.395E6 + 3.41E5 -> Rnow all you have to do is type in and calculate ...

[ENTER]

you should get about 4778 m/s which you can change to km/s if that's the way you need to express it.