To make our explicit equation, what we need to do is first find a "zeroth term."
Since we're subtracting two each time, we can take that in reverse and say that our zeroth term would then be 7.
Then you would subtract 2 n times from 7 to find any term n,
Another thing to note is that we can only use natural numbers as our term number. (1, 2, 3, 4, 5...we can't use 0, can't use negatives, can't use fractions...etc.)