Think of variable K as number of trees planted and variable J as number of minutes it takes to plant the trees.
K = _J + _
For every 4 trees planted it takes 2 minutes to plant them, so we now have -4/2. 4 is negative because we don't have an unlimited amount of trees to plant. With this being said, we can use this fraction as J.
K = -4/2J + _
We lose 4 trees every 2 minutes, but how many trees did we initially start out with? According to the graph, we started with 28 trees, so K = -4/2J + 28.
Now we can test this equation out by picking a random dot on the graph: 24/2.
24 = -4/2(2) + 28
24 = -4 + 28
24 = 24
This statement is correct, so our equation is correct.