Shabana has to stitch 35 dresses. So far, she has stitched 21 dresses. What fraction of dresses has she stitched?

Total number of dresses to be stitched = 35

Number of dresses stitched so far = 21

Fraction of dresses stitched = $\dfrac{\text{Dresses stitched}}{\text{Total dresses}}$

= $\dfrac{21}{35}$

Hence, the required fraction = $\dfrac{21}{35}$.