Diego has 7 packs of markers. Each pack has x markers in it. After Lin gives him 9 more markers, he has a total of 30 markers

For this case we must find:

x = the number of marbles in a package.

For this, according to the statement we have the following equation:

7x + 9 = 30

Clearing x we have:

7x = 30-9

x = 21/7

x = 3 marbles

Answer:

Each pack of marbles contains 3 marbles