What is the equation for the value (in dollars) of the account after t years if it doubles every 15 years?
a) f(t) = 9500 × 2{t/15}
b) f(t) = 9500 × 2{15/t}
c) f(t) = 9500 × (1 + {t}{15})
d) f(t) = 9500 × (1 + {15}{t})