Find an equation for the nth term of the arithmetic sequence. -20, -16, -12, -8, ...

The difference each time is 4 so first we must do 4n which in a sequence equals 4, 8, 12... but the actually sequence is -20, -16, -12... so to turn 4 into - 20 we have to -24 and the same goes for 8 into -16 and 12 into -12. Thus meaning the nth term is 4n - 24.