A boy uses a spectacles of focal length -60 cm. Name the defect of vision he is suffering from. Which lens is used for correction of its defect ? Compute the power of this lens.

please someone answer my question.

If he is using a spectacle of Negative focal length .. it shows that he is using a concave lens , so it is used for myopia , which is also known as short sightedness . 
Nearsightedness occurs if the eyeball is too long or the cornea, the clear front cover of the eye, has too much curvature. As a result, the light entering the eye isn’t focused correctly and distant objects look blurred.

The power of the lens will be - 
$$\begin{gathered} Power of a lens = \frac{1}{focal length} \\ Power = \frac{1}{-60cm}=\frac{100}{-60m}=- 1.66dioptre \end{gathered}$$