An initial deposit of $200 is made into an account that pays 4.2% annual interest. What is a model to represent the balance in the account after x years?

You would use the equation y = A (1+r) ^t

A = Original amount = 200

r = interest rate = 0.042 (when converted from percent to decimal)

t = time = x

Plug them in and you get the model: y = 200 (1+0.042) ^x

or just simplify the parentheses to (1.042)