With this kind of equation, you want to set up a ratio. So, in this case, let's say the top will be the height of the object, and the bottom in the shadow the object casts. So, it'll be x/23.5=6/4.7. You then cross-multiply and divide. So, you multiply 23.5*6, which is 141. Then you divide 141/4.7, which is 30. Hope that helped!
