Line Plots · Superchallenge problem

A line plot shows $12$ ribbons, each $\dfrac{1}{4}$, $\dfrac{1}{2}$ or $\dfrac{3}{4}$ foot long. There are twice as many X's above $\dfrac{1}{4}$ as above $\dfrac{3}{4}$. Laid end to end, the ribbons are $5\dfrac{1}{2}$ feet long. How many X's are above $\dfrac{1}{4}$?