Given that 2 similar signs have a scale factor of 5:3 and the larger sign is 45 ft, then the smaller sign will have the height given by:
scale factor=(height of large sign )/(height of smaller sign)
let the height of smaller sign be x, plugging in the values we get:
5/3=45/x
solving for x we get
3/5=x/45
hence
x=3/5×45
x=27 ft
The height of smaller sign will be 27 ft