Respuesta :
ratio and proportaion
assuming the shadow to the actual height is constant
shadow:actual height=12ft:40ft=12/40=3/10=3ft:10ft
so
3ft:10ft=?:21ft
solve
3ft/10ft=?/21ft
times both sides by 21ft
63ft/10=?
6.3ft=?
the shadow is 6.3ft
assuming the shadow to the actual height is constant
shadow:actual height=12ft:40ft=12/40=3/10=3ft:10ft
so
3ft:10ft=?:21ft
solve
3ft/10ft=?/21ft
times both sides by 21ft
63ft/10=?
6.3ft=?
the shadow is 6.3ft