Answer: The gravitational acceleration on planet X is 5 N/kg
On Earth (with the gravitational accelartion g_E) the mass of 2kg will correspond to

On planet X we are told the same measure is only 10N. Since there is a proportional relationship between g and F, we can calculate g_X:

Gravitational potential energy =
(mass) x (gravity) x (height)
= (5.8 kg) x (9.8 m/s²) x (2.5 m)
= 142.1 Joules (C)
Ok. PEMDAS tells us to take care of the square first. When we do that, the denominator becomes
(6.4)^2 x 10^12
= 40.96 x 10^12 .
Now it's just a matter of mashing out the fraction.
The 'mantissa' (the number part) is
6/40.96 = 0.1465
and the order of magnitude is
10^24 / 10^12 = 10^12 .
Put it all together and you've got
1.465 x 10^11 .