Copper is composed of two naturally occurring isotopes: Cu−63 (69.170%) and Cu−65. The ratio of the masses of the two isotopes is 1.0318.
x*0.69170+x*1.0318*(1-0.69170)=63.546
x=answer
What is the mass of Cu−63?
I believe you also need to know the mass of the mixture occurring in nature.
I just asks me to figure out the mass of Cu-63? the mass of nature is 69.170% for Cu-63 and for Cu_65 it is 30.83%
I don't think you understand what I need. The ABUNDANCE of 63 is 69.170% and the ABUNDANCE of 65 is 30.83%. But you don't have the mass of anything; i.e., you don't have the mass of 63 or the mass of 65 or the mass of the isotope as it occurs in nature (the mixture). Here is as far as I can go.
Let x = mass Cu63
and y = mass Cu65
and z = mass of naturally occurring isotope.
--------------------
x(0.69170)+(y)(0.3083) = z
Three unknowns and you can't solve the equation. You can relate x and y with the ratio data. You don't say which ratio is which but I presume that is mass Cu65/mass Cu63 = 1.0318 and that lets us write
y/x = 1.0318 or y = 1.0318x and that can be substituted into the above for
x(0.69170) + (1.0318x)(0.3083)= z.
I believe you need another piece of information, namely z, to solve the equation.