I'm missing something on this problem:
"As you go deeper into a cave, the light intensity gradually decreases until it becomes very dark. Let L(d) denote the light intensity in a certain cave L (measured in cd/sq. m) at a given depth d (measured in m). Write an equation that represents the following statement:
The light intensity 4m inside the cave is 3000 cd/sq. m less than the light intensity at the entrance to the cave. "
I wrote L(4)-L(0)/4=-3000
But it turned out to be wrong and I don't know what it is. What did I do wrong?