Refer to the picture above. HELP this is geometry

Erin bought christmas cards for $2 each to send to her family and friends. which variable is the dependent variable?

Me get the answer and explain to me the steps to solve it would be greatly appreciated : )

You open a savings account with a $400 deposit. each month after that, you deposit $25. write an explicit rule to represent the amount of money you deposit into your savings account. how much money will you have in the account on month 12? pleasseee : (