Aprobe orbiting venus exerts a gravitational force of 2.58 × 10^3 n on venus. venus has a mass of 4.87 × 10^24 kg. the mass of the probe is 655 kilograms. to three significant digits, the probe is 9.08 × 10^6 m from the center of venus.

So this is the info that's given to us:
m1 = 4.87 x 10^24 kg
m2 = 4.87 x 10^24kg
F = 2.58 x 10^3 N

Now we can use this equation to solve: 

You may be asking what g is. Well, it is equal to 6.67x10^-11 m3 /kg s2. G is gravitational constant. So :

 

As you can see we only have one variable, so we solve for r! 



I hope this helps you out. I remember when I was first learning Newton's law of universal gravitation and I had some trouble. But with some practice, I got better. =) 

Initial velocity,  u = 4.9 m/sfinal velocity = v m/sinitial height,  h₁ =  245 m    final height, h₂ = 0a = -9.8  m/s²time taken = t secondss = ut + 0.5at²⇒  (h₂-h₁) = ut + 0.5at²⇒  0-245 = 4.9t + 0.5×(-9.8)×t²⇒ -245 = 4.9t - 4.9t²⇒ 4.9t² -4.9t -245 =0solving it, we get   t = 7.59sv  = u +  at = 4.9 -9.8×7.59 = 4.9 - 74.38 = -69.48 m/svelocity is  69.48 m/s downward