Question 131490
130kg
20% Mg= 20% * 130 = 26 
80%Al= 80% * 130 =104 
if you add them it should be the total mass 130
the question now is what is the amount that i need to put for the Mg to raise it to 35% insted of 20%?
 x/130=0.35 it should be 45.5kg of Mg added , and the Al will be 84.5 kg