The exponential function that represent the value of Mary's Computer is:
[tex]f(t)=520(0.25)^{t} [/tex]
for t=0, we get:
[tex]f(0)=520(0.25)^{0} \\ \\
f(0)=520(1) \\ \\
f(0)=520[/tex]
Interpretation:
The exponential function shows the value of her computer after t years, so by replacing t=0, we will get the value of computer the year she bought it.
Thus, the value of computer when Mary bought it was $520.