A Now-Next approach replaces algebra with simple arithmetic. It avoids using variables. All that needs to be done is to define a starting point and then an operation that takes the calculation to the next stage. The same operation is repeated to take the calculation to the stage after that.
Example: Stacking cards. We start with one card. That’s the Now. To get to the Next we double the number of cards already stacked (which was one card) and add that number to the stack. So double the number already on the stack gives us 2, so we add 2 cards to the stack giving us 3 cards. This is the new Now. Repeat the procedure: double the number of cards on the stack (3) to get 6 and add this number of cards to the stack, so we add 6 cards to the stack to make 9. This is the new Now.
At the next stage we add 18 cards to get 27. Then we add 54 cards to get 81.
If we make a table showing the progress then we have established a function without using algebra.
In the example the operation involved multiplication and addition. It could have simply involved adding or subtracting. But the principle is the same. We have a starting point and an arithmetic operation to take us to the next stage.