How do I solve this?

Q6 A space capsule is descending from orbit. After 90 seconds, it is 10,000m above sea level and falling at 400m per second. a Write a linearization for h(t), the height of the capsule at time t. b Use a to predict when the capsule will splash down into the ocean. C Do you expect that your answer to b is an overestimate or underestimate? Explain