Charmander is furious; he kicks a rock with a mass of 20.0 kg, straight up in the air. The net force on the rock is 230N.
a) How much does the rock weigh?
b) How hard did Charmander kick the rock?
c) What is the acceleration of the pokémon

(a) The rock has a weight w according to

w = m g

where m is its mass and g = 9.80 m/s² is the magnitude of the acceleration due to gravity. So

w = (20.0 kg) (9.80 m/s²) = 196 N

(b) Charmander kicks the rock with an upward force (magnitude f ) that overcomes the weight of the rock, and the net force on it is 230 N. This means

f - w = 230 N

f - 196 N = 230 N

f = 426 N

(c) I think the question is supposed to say, "What is the acceleration of the rock," and not asking about Charmander's acceleration. By Newton's second law, the net force on the rock is equal to its mass times its acceleration:

230 N = (20.0 kg) a

a = (230 N) / (20.0 kg)

a = 11.5 m/s²