$1,000 is deposited into a savings account. Interest is compounded annually. After 1 year, the value of the account is $1,020. After 2 years, the value of the account is $1,040.40. This scenario can be represented by an exponential function of the form f(x)=1000(b)^x , where f(x) is the amount in the savings account, and x is time in years. What is the value of b ?