Question 887872
Let x,y be the unknown numbers.
We are given
(1) x + y = 210 
(2) x = y^2
Put (2) into (1) and get
(3) y^2 + y = 210 or
(4) y^2 + y - 210 = 0
This factors into
(5) (y-14)*(y+15) = 0 giving us two values of y 
(6) y = {14,-15)
Now use (2) to get the corresponding values of x as
(7) x = {196,225}
Let's check this with (1).
Is (196 + 14 = 210)?
Is (210 = 210)? Yes
Is (225 + (-15) = 210)?
Is (210 = 210)? Yes
Answer; There are two pairs of numbers (196,14) and (225,-15).