Four-fifihs of 'n' plus 8 is 18

25/2 or 12.5

(4/5) X n + 8 = 18

(4/5) X n = 18-8 = 10

n = (10 X 5)/4

n = (5 X 2 X 5)/(2 X 2)

n = 25/2 = 12.5