There are two ways you can solve this. You can do:
1600 · 0.05 = 80
Then you add this to your current rent
1600 + 80 = 1680
$1680 will be your rent next month
Another way to do it is:
1600 · 1.05 = 1680
The "1" in 1.05 keeps the 1600, and the .05 adds the additional rent for next month.
The answer is C
x = 0.05(1600) + 1600
x = 80 + 1600
x = 1680