Given:
Initial number of chocolates in the box = 30
Colton ate 2 chocolates each night.
To find:
The equation for the number of chocolates remaining in the box t days after Colton's birthday.
Solution:
Let C be the chocolates remaining in the box and t is number of days after Colton's birthday.
Colton ate 2 chocolates each night. It means, the remaining number of chocolates decreased by 2 per day.
Initial number of chocolates in the box is 30 and it decreased by 2 per day. So, the equation for remaining chocolates is

Therefore, the required equation is
.