**Solution:**

Since, the three persons start walking together.

Therefore, The minimum distance covered by each of them in complete steps = LCM of the measures of their steps

= LCM (80, 85, 90)

80 = 2 x 2 x 2 x 2 x 5= 2^{4} x 5

85 = 5 x 17

90 = 2 x 3 x 3 x 5 = 2 x 3^{2} x 5

=> LCM (80, 85, 90) = 2^{4} x 3^{2} x 5 x 17

= 12240

=> Each person should walk a minimum distance of 12240 cm in complete steps.

Morning walk is good for healthy life.