algebra
posted by Sue .
Adam is 3 times as old as Cynthia and Fred is 16 years younger than adam. One year ago, Adam's age was twice the sum of Cythia and Freds age. Find the present ages.
I have
a=3c f=a16 a1=2(c1 + f1)
and I don't understand what comes next and why

a=3c
f=a16
a1=2(c1 + f1)
so far, so good. Now start substituting. First, get rid of a:
f = 3c16
3c1 = 2(f+c2)
Now get rid of the f:
3c1 = 2((3c16)+c2)
3c1 = 2(4c18)
3c1 = 8c  36
5c = 35
c = 7
so, f = 3c16 = 5
and a = 3c = 21