2) How much PURE copper must be added to 50.255kg of an allow containing 12% copper to raise the copper content to 21%

let x=amt of pure copper to add:

12%*50+100%x=21%(50+x)

6+x=10.5+.21x

.79x=4.5

x=5.7

amt of pure copper to add: 5.7 kg

Step-by-step explanation:

set each factor equal to 0

4x-3 = 0

2x-1 = 0

solve for x.

4x-3=0

4x=3

x= 3/4

solve for x. 

2x-1= 0

2x= 1

x= 1/2

your answer should be 1/2 is less than or equal to x and 3/4 is greater than or equal to x