SOLUTION: Phil is 28 years older than Tom. Six years ago the sum of their age was 36. How old are they now?

From the condition, you have these two equations in 2 unknowns


P = T + 28              (1)
(P-6) + (T-6) = 36.     (2)


Simplify eq(2) :


P + T = 36 + 6 + 6,   or

P + T = 48              (2')


From eq(1), substitute expression for P into eq(2'), replacing (excluding) P. You will get


(T + 28) + T = 48.


Simplify and solve for T:


2T = 48 - 28 = 20  ====>  T = 20/2 = 10.


Answer.  Tom is 10 years old.  Phil is 10 + 28 = 38 years old.


Check on your own that all conditions of the problem are satisfied.