S + 5 = S
For what does S stand?
Note: The above equation has no solution, so there's something wrong with the logic
of it. How did you arrive that this equation?
Try studying the general methodology of this sort of exercise here
. Then, following the logic explained there (and in what was given to you within the exercise itself):
Joe is defined in terms of Sally, so:
i) Pick a variable to stand for Sally's age now
ii) Write an expression, in terms of the variable in (i), for Joe's age now
iii) Write an expression, in terms of the variable in (i), for Sally's age after she's fifteen years older.
iv) Write an expression, in terms of the expression in (ii), for Joe's age after he's fifteen years older.
v) Using the expression in (iii) and the variable in (i), write an equation for "(Joe's age after fifteen years) is (three) times (Sally'es age now)".
vi) Solve the equation
vii) Use the definition in (i) to interpret the answer to (vi).
If you get stuck, please reply showing your work for each of the steps above, as far as you were able to get.