Dear Sowedi,

please have a look at the diagram of the link.

This is just the one you look for.

http://www.thefoa.org/tech/ref/basic/dB.html

by the way: this looks like a home work excercise....

Provided no other information, the power drops exponentially... staring with 1 dBm (miliWatt), continuously draw a linear dropping line in dB scale, with slope equal to the loss per unit length...

If I understand the information correctly, you can calculate as shown in the Excel file attached.