In the question it is given that Louie has 20 more than half as many baseball cards as Gerardo does.So,
Let us assume that the number of baseball cards Gerardo has = X
Number of baseball cards that Louie has = 20 + X/2
Also the total number of baseball cards Louie and Gerardo has together is 350.
Then,
X + X/2 + 20 = 350
X + X/2 = 350 - 20
X + X/2 = 330
3X/2 = 330
3X = 330 * 2
3X = 660
X = 660/3
= 220
Number of baseball cards Gerardo has = 220
Number of cards Louie has = 130.