Question 694599
Brass = Copper + Zinc

Let Zinc be x
copper = 3x/5

Brass = x+3x/5

8x/5

a) what is the mass of copper in 175g of brass?

175= 8x/5
175*5=8x
175*5/8 = x 
109.38--->Zinc

Copper = 3x/5 ---> 3*109.38/5
65.63----> Copper

b)what mass of brass contains 90 g of copper?

Brass = 90*5/3
=150 grams

c) what mass of brass contains 50g of zinc?

brass = 50 +(3/5)*50

=50+30
=80 grams