X= QUEEN CITY COFFEE %
1-X = KENYA COFFE %
11.60(1-X) +14.3X =13.91
Opening parenthesis
11.60-11.60X+14.3X=13.91
Subtracting 11.60 both sides of equal sign and rewriting equation.
14.3X-11.6X =13.91-11.60
2.7 X =2.31
DEVIDE BOTH SIDES BY 2.7 TO SOLVE...

lets take
X= Number of books that sylvia sold = 100%
Now, Sam's sold 15% more books than sylvia which makes it that sam's sold (100%+15%) =115%
when taking % off( simply you devide by 100-----> 115/100 =1.15) that amount of books sold by Sam's =1.15X
1.15x=69 books
X=60=...

Variable linear equation: y=ax+b, where a and b are any number , you can also called constant
and y and x are variable...