A tree casts a shadow of 12 meters when a 5meter post nearby casts a shadow of 6 meters find the height of the tree.

Use equality of proportions object:shadow

x:12 = 5 m : 6 m

which means
x/12=5/6

Cross multiply:
6x=5*12

Solve for x
x=60/6=10

So the tree is 10 m tall