Where is this formula from: r = (nXY - XY) / (nX - (X)) (nY - (Y))

And how did you calculate the following according to this information

Year	Advertising expenditure (X)	Sales revenue (Y)
	(000s)	(000S)
2017	2	100
2018	5	70
2019	4	90
2020	6	60
2021	3	80

n = 5 X = 18 Y = 22 XY = 1080 X = 4560 Y = 8720