Let L represent the number of ribbons Lily has and D be the amount of ribbons Dora has.
Since Lily has 4 fewer ribbons than Dora, the amount of ribbons Lily has can be represented as this:
L = D - 4
Because Lily has 7 ribbons, you can plug in 7 for L:
7 = D - 4
When you solve for the amount of ribbons Dora has (D), which is done by adding 4 to both sides, you get D = 11.
Therefore, Dora has 11 ribbons.