Question 521132
let r be Renee's age, p be Paulo's age and t be Peter's age.

the sum of their age is 21, means  r + p + t=21

Renee is five years older than Paulo, so  r= p + 5
Renee is seven years older than Peter, so r= t + 7

r=r, so p + 5= t+ 7
        p - t = 2   (1)

we know, r + p +t= 21
since r= p+5,   so p+5 + p + t=21
                   2p + t = 21-5 =16         (2)

by adding up the two equations (1) and (2)
we have,    (p-t) + (2p + t)= 2 + 16 
            3p=18
 so p=6
   r= p + 5 = 6 + 5= 11
   t + 7= r, so t= r - 7
                 =11-7
                 =4

so, Renee is 11 years old, Peter is 6 years old and Peter is 4 years old.