Question

In six years, jill will be twice amanda’s age. one year ago, jill was nine times amanda’s age. how old is jill now?

Answer 1

Jill = J
Amanda = A

J + 6 = 2 (A+6)   ..... .........................   J + 6 = 2A + 12
J -1 = 9 (A-1)       ...............................   J - 1  = 9A -9___      (- )   

We need to elimiate both of those formula , the result will be
7 = -7A + 21
7A= 14
A = 2  >>>>> subtitute this to any formula above

So, Jill's age now would be:  
J + 6 = 2 (A+6)
J + 6 = 2 (2+6)
J + 6 = 16
J = 10