Electrical Formula Review

Formulas to review:
- Voltage drop percentage over a distance with giving power source and material.

What type copper wire will be needed to safely wire a tree house light 175 ft from the main house supplied by a 120 volt power supply with 12 Amps of current?

Formula is:
CM =2(Km)(L)(I) / Vd

Sort out the values
(Km): Material value: Copper: material value : 12.9
(L): Distance: 175 ft
Vd : Voltage :120 * 0.03 = 3.6V (at 3% safety value)
I = 12A

(2)(12.9)(12)(175) / 3.6 = 15,050 CM

Looking up the wire gauge table. Minimum required size is 8 AWG at 16510 CM.