If at January x = 0, then as you go through the months, x will increase by 1. As they make 1000 each month, multiplying the month by 1000 will show you how much they make
So part of the equation is 1000x
Next, you know that they start with a £25,000 profit, so you need to add it on to the profits you make each month. So the second part needs to be + 25,000
The final function is therefore 1000x + 25,000, which is D