Aphone company needs to know how tall a cell tower is, so it decides to use a 4 m pole and shadows cast by the sun, as shown in the diagram. both shadows end at point b.

what is the height of the tower?

The question above is a ratio problem so since both shadows end at point B, then the towers are proportional.
Start with 40:5 and reduce it to 8:1. Now, for every 8 meters of the big tower, the little tower increases one.
Now since the little tower is 4 meters, the big tower will be 36 meters.
I hope my answer helped you.