y = m x + b is a linear equation.
This equation is in the slope - intercept form, where m is the slope and b is y - intercept.
For example: y = 2 x + 5
In this equation: m = 2 ( the slope ) and b = 5 ( the line intercepts y-axis at the point ( 0, 5 ) ).
Answer: Choice D

This basically says "the nth term is found by computing math, aka evaluating some function, based on the (n-1)th term".
As an example, we could have a function that simply squares the input
Let's say we started at 5. It squares to 25 which in turns squares to 625, and so on. Each new term is based on the old term. Namely, we squared the old n-1 term to get the new nth term.
In order to figure this out, you are going to do the math backwards. If the perimeter of the entire field is 96 meters, you will want to remove 16, which will give you 80 meters. You will then divide this by 2, giving you 40 meters. The width of the field will be 40 meters. That means that the length of the field is going to be 56 meters.