Todd has x amount of gold fish
Andrew has x + 10 amount of gold fish
They have 50 in all
x +(x+10) = 50
2x + 10 = 50
2x +10 (-10) = 50 (-10)
2x/2 = 40/2
x = 20
Todd has x amount of goldfish, so he has 20 goldfish
Andrew has (x + 10) amount of goldfish, so he has 30, because 20 + 10 = 30
hope this helps