Answer: f(x)=20(1.0125)^t
Explanation:
use the formula P(1+r)^t when considering exponential growth (make it 1-r if decay)
P - principal (initial) value
r - growth rate (as a decimal! so divide by 100)
t - time (can be years, months, days, etc)
so now that we know the formula, just plug in everything you know!
P=20, r=0.0125, t=x
so the function is
20(1+0.0125)^t or 20(1.0125)^t
since we dont have a defined time, that becomes the variable for x, the one we can manipulate, so if they ask for 10 years, just replace t with 10!