No, wearing sunscreen won't let you tan. The whole purpose of sunscreen is to protect your skin from sun rays. You can start to become tan if you dont have much sunscreen on - its happened to me.
Answer:
The answer is 34.67 kilograms force
The strength of the gravitational field is given by:

where
G is the gravitational constant
M is the Earth's mass
r is the distance measured from the centre of the planet.
In our problem, we are located at 300 km above the surface. Since the Earth radius is R=6370 km, the distance from the Earth's center is:

And now we can use the previous equation to calculate the field strength at that altitude:

And we can see this value is a bit less than the gravitational strength at the surface, which is

.
It will be a little bit less because of evaporation i learned that in third grade and your in high school that is sad