A metalworker has a metal alloy that is 30% copper and another alloy that is 60% copper. How many kilograms of each alloy should the metalworker combine to create 60 kg of a 54% copper alloy? The metalworker should use blank kilograms of the metal alloy that is 30% copper and blank kilograms of the metal alloy that is 60% copper.

Y  = -8x + 56
2y= -2x + 56 (you want to get rid of one variable then solve for it then solve for                         the other)

-2(y=-8x+56)
2y=-2x+56

-2y=16x-112
2y=-2x+56     (see how multi the first equation by -2 gets the y's to cancel so                     can solve for x. Now sum up the equations)
0= 14x-56
x= 4

now plug x=4 into any original equation Y=-8x+56
Y = -8(4)+56
Y=24

hope this helps