SOLUTION: Carly is 5 years older than Dan.In 10 years the sum of their age will be 75.Find the age of each man now

C - D = 5.             (1)
(C+10) + (D+10) = 75.  (2)


It is equivalent to

c - D =  5,            (3)
c + D = 55.            (4)

Now add the equations (3) and (4) and see what will happen.