Calculate percent of 2 isotopes?

Question

Can someone please explain how to do this question. I cannot remember how to do this for 2 unknown percents.

An element consists of two isotopes of mass 6.2882 and 7.9032 amu. If the average atomic mass of the element is 7.432 amu, calculate the percent abundance of the first isotope.

Answer 1

Solve the simultaneous equations:

(a x 6.2882) + (b x 7.9032) = 7.432 and

a + b = 100