The first thing we must do for this case is to define variables.
We have then:
x = Ashley age
y = Jessica age
We write the system of equations:
x + y = 71
x = y-15
Solving the system we have:
(y-15) + y = 71
2y - 15 = 71
y = (71 + 15) / (2)
y = 43 years
Then, for x we have:
x = y-15
x = 43-15
x = 28 years
Answer:
Ashley is 28 years old.
Jessica is 43 years old.
