What is the sum of two numbers 20 the product of the numbers is 75?

If you mean that the sum of the two numbers is 20 and the product is 75, then

X+Y=20 and XY=75

solving for Y and substituting: Y=20-X and XY=X(20-X)

then X(20-X)=75 and 20X-X2=75

(20X-X2)-(20X-X2)=75-(20X-X2)

then X2-20X+75=0

factoring (X-5)(X-15)=0, so X=15 or X=5

if X=5, then Y=75/X=15

if X=15, then Y=75/X=75/15=5