Two questions (one just checking formula)

To solve this question:

Suppose you deposit $100 in an account that earns 0.5% each month. You make no withdrawals from the account and deposit no more money into the account. How much money will you have in the account after 4 years?

Do I use A = P(1 + rt) to solve this question? If so, is my answer right:

A = P(1 + rt)

A = 100[1 + (.5 x 48)]

A = 100[1 + 24]

A = 100[25]

A = 2500

Second question: (I don't even know where to begin & I have to show my work!)

A projectile is fired directly upward with amuzzle velocity of 860 feet per second from a height of 7 feet above the ground.

a. Determine a function for the height of the projectile "t" seconds after it's released.

b. How long does it take the projectile to reach a height of 100 feet on its way up?

c. How long is the projectile in the air?