A 10-ft vertical post casts a 20-in shadow at the same time a nearby cell phone tower casts a 120-ft shadow.
How tall is the cell phone tower (ft)?

x:       y:  

-1         4

0         4

1         6

2         18

3         20  

4 inches will get you 10.16 centimeters, but you can either do 10.1 or round up to 10.2. good luck and hope this : )