About F.1 Maths...!!PLZ

Let the weight of copper be x kg,
the weight of zinc be y kg.
given that x:y=5:7 ……....(1)
and 2x=y+12 ……..(2)
from (1), let x/5=y/7=k we have
x=5k, y=7k ………(3)
substitute (3) into (2),
10k=7k+12
3k=12
k=4
Thus, x=20, and y=28
The answer is the amounts of copper in the alloy is 20kg.


(5x)[2x(x+3y)+x(y-7x)]
=(5x)(7xy-5x2)
=35x2y-25x3
=5x2(7y-5x)

Besides, may God bless your family and wishing you success in your study.

1.Let c kg and z kg be the weights of copper and zinc in the alloy
respectively.
c kg: z kg=7:5
5c=7z
c kg+12kg = 2z kg
c+12=2z
z=5c/7
c+12=2(5c/7)
7c+84=10c
3c=84
c=28
There are 28 kg copper in the alloy.

(5x)[2x(x=3y)+x(y-7x)]
=10x sq.(x=3y)+5x sq.y-35x cube.
(What is (x=3y)?)