Thread: HELP!! Maths question!

A cable used to send data has an attenuation where power drops by a factor of 10 every 10 km. If the input power is 1 W, and the receiver can detect signals with a power of 10^-4 W or more, what is the longest cable that can be used without a regenerator?

Find the signal power at the receiver if the input power is 1W and the cable length is 10km, 20km, 30km, 40km.