Question 751511
a lamppost casts a shadow that is 16 feet long a 2.5 foot high mailbox casts a shadow that is 4 feet long how tall is the lamp post
both cast shadow same time 
it means angle of elevation at same time will be same and shadow will be also in praposnate 
it will have conditions of two similar triangle 
ratio  of the corresponding side  of similar triangle  are equal
let height of lamp post is x
x/16=2.5/4  by cross multiply  we will get 
4x=16 multiplied by 2.5
x=16 multiplied 2.5/4
x=10
height of lamp post is 10 m ANSWER