algebra problem from chemistry class

[dln1128]

this problem is out of my chemistry book. The chemistry part I understand, it's once I get the equation set up I'm not sure how to solve it.

the full question is

Chlorine has two isotopes 35/17Cl & 37/17Cl which have masses of 34.96885 u and36.96590 u, respectively. Its average atomic mass is 35.453 u. What are the percent abundances of the two isotopes?

***please not the 35/17 is not a fraction. the top number stands for the mass number the bottom number is the atomic number****

To calculate the average mass of an atom of an element, you multiply the fractional abundance of each isotope by its mass and then add the products.

For this problem I let the fractional abundance of 35/17Cl be x, ad the fractional abundance of 37/17Cl 1-x.

I then set us the equation

34.96885u(x) + 36.96590 u (1-x) = 35.453

from this point on im not sure how to proceed.
If someone could show me how to solve this problem step by step it would be greatly appreciated. Please do not assume I know anything when showing the explanation. The nre steps shown in hte explanation the easier it is for me to understand. Thanks in advance for whoever answers this

 

[skeeter]

let A = mass of the less massive isotope
B = mass of the more massive isotope
C = average mass

Ax + B(1 - x) = C

solving for x ...

Ax + B - Bx = C

Ax - Bx = C - B

x(A - B) = C - B

x = (C - B)/(A - B), or
x = (B - C)/(B - A) if you desire (+) values in the numerator and denominator

I get x = 0.7575674...