The average rate of change between two input values is the total change of the function values (output values) divided by the change in the input values.
The recursive rule is

.
The iterative rule is

The recursive rule is given by the formula

, where d is the common difference. Our common difference is -4, which gives us the recursive rule above.
The iterative rule begins with the formula

, where a₁ is the first term and d is the common difference. Our first term is 10 and our common difference is -4:
2.25 x 1000 = 2250.
That's how much yds of ribbons he needs.