Given:
6 out of 15 customers order a chicken sandwich
270 customers
This is a problem of ratio and proportion:
a/b = c/d where ad = bc
6/15 = x/270
6 * 270 = 15x
1,620 = 15x
1620 / 15 = x
108 = x
The restaurant should predict to serve 108 chicken sandwich to the 270 people.