In this problem
we have an exponential growth function of the form
where
y is the total amount in the saving account
x is the number of years since the year 2013
r is the rate
a is the initial value
where
a=$15,500
r=4.4%=4.4/100=0.044
year 2031 -----> x=2031-2013=18 years
substitute in the equation