A 10-ft vertical post casts a 4-ft shadow at the same time a nearby cell phone tower casts a 6-ft shadow. How tall is the cell phone tower?

We can set up a proportion to solve this problem. Let x be the height of the cell phone tower. The proportion is 10/4 = x/6. We can cross-multiply to solve for x: 4x = 60. Dividing both sides by 4, we get x = <<15=15>>15. The height of the cell phone tower is 15 ft. Answer: \boxed{15}.