Question

Could someone help me? I'm not sure at what I did wrong

Answer 1

the middle step should not have an "x" in it for the amount of copper
it should read 0.3*400 (which is 120)

Answer 2

sorry i got 'cut off'

x = amount of 10% alloy
so amount of copper in this = 0.10x grams

your error in in the second line
the amount of copper in the 30% alloy is 0.30(400) not 0.30x(400)

Answer 3

do you follow that ok?

Answer 4

Is the .20(x+400) correct.
I understand what I did wrong @welshfella

Answer 5

yes that is correct

so the equation will be the sum of the first 2 amounts of copper = 0.20(x + 400)