The sum of two numbers is 9. if one number is subtracted from the other, the result is 3. find the numbers

Will give brainliest sum of arithmetic series (sigma notation) find the numerical answer to the summation given below. (image shown below)

Ineed to know the answer to this algebra question.

Rhombus adef is inscribed into a triangle abc so that they share angle a and the vertex e lies on the side bc . what is the length of the side of the rhombus if ab=c, and ac=b.