Penny Pincher gets a present of $100. She puts it into a savings account. Thereafter, she adds $4 more at the end of each week. a. Define a variable for the number of weeks and write an expression for the number of dollars she has put into her account.

b. The savings account pays a certain interest rate when the amount in it is from $200 up to, but not including, $500. For what numbers of weeks will Penny's amount be in this range?

c. The interest rate is much higher when the balance is over $1000. For what range of weeks will the amount be over $1000?​