Let k be the spring constant.
• When the spring is compressed by 11 cm = 0.11 m, it stores
1/2 k (0.11 m)²
of potential energy.
• When it's compressed by 66 cm = 0.66 m, it stores
1/2 k (0.66 m)²
of potential energy.
Then the ratio of these potential energies is
(1/2 k (0.66 m)²) / (1/2 k (0.11 m)²) = 36
which is to say, the spring stores 36 times more energy when it's compressed by 66 cm compared to 11 cm.
