To answer this youd have to set up a proportion. 5/2 is the ratio of weight on earth and mars respectively. The other side has to have the same ratio where 125lbs is the weight on earth and x is the weight on mars. The equation would look like 5/2=125/x. Youd have to cross multiply, and would get (125)(2)=5x. Solve for x to find the weight on mars