Dave has $11 and he buys a book for $8 but he spends an equal amount of money on 2 cards. Let's model this problem with an inequality.
x = $ spent on one card.
2x + $8 ≤ $11
Let's subtract $8 from both sides.
2x ≤ $3
Divide both sides by 2
x ≤ $1.5
Dave can spend at most $1.5 on each card.