The right system of equations to describe the situation would be on the form:
x1 = 8000 + y1*t
and
x2 = 8000 + y2*t
where x1 and x2 represents the total money of Imogene and her friend respectively at the end of t years.
Now for the value of amount earned, y1 and y2:
y1=8000*0.08
y2=2000*√(t-2)