Weight vs Mass On Moon and Mars Imperial Units

[BigJon]

Homework Statement

Moon's gravity is 5.31ft/sec^2 An object has the weight of 3.5 lb-f on the moon. What is its lb-m
What is the lb-m and lb-f on Mars with gravity of 12.1 ft/sec^2.

Homework Equations

w=mg=mg/gc

gc= gravitational constant----> 32lbm*ft/sec^2 for earth

The Attempt at a Solution

So I understand mass is the same everywhere. Also lb-m and lb-f are the same numerically on Earth but not on other planets?

Im just really confused with imperial units because i don't understand when to use or not use the gc.

 

[voko]

$1 \ \text{lbf} = 32.174 \ \frac {\text{ft} \cdot \text{lbm}} {\text{s}^2}$.