Average height (in cm) of the girls whose heights are 155 cm and above is about-

Take value of class interval 155 - 160 and 160 - 165 i.e. 157.5 and 162.5.
Multiply them by their respective frequency and then divide by total no. of girls.
$$\eqalign{ & = \frac{157.5 \times 6 + 162.5 \times 5}{11} \cr & = \frac{945 + 812.5}{11} \cr & = \frac{1757.5}{11} \cr & = 159.8 \text{ cm} \cr}$$