Let's denote the number of roses Mary cut from her garden as x . Initially, there were 6 roses in the vase. Mary cut x roses, so the total number of roses in the vase became 6 + x . After cutting some roses, the total number of roses in the vase became 11. Therefore, we can write the equation:
6 + x = 11
To find the value of x , we need to solve this simple equation:
x = 11 - 6
x = 5
Mary cut 5 roses from her flower garden.
\boxed{5}