Answer: 63.13%
Step-by-step explanation:
given data:
copper = 21.8%
0.13%x + 29%(140-x) = 21.8%(140)
open the brackets
0.13x + 40.6 - 0.29x = 30.5
collect like terms
0.13x - 0.29x = 30.5 - 40.6
β0.16x = β10.1
divide both sides by β 0.16
β0.16x / β 0.16 = β10.1 / β0.16
x = 63.13%