Since rays are converging, so it is a converging lens i.e., convex lens. Rays coming from sun are considered to be coming from infinity and a converging lens converges all the incident rays from infinity at focus.
Convex lens forms real image of a distant object and its focal length is positive in sign.
So, here focal length =20‌cm=0.2m
Power of convex lens gives the degree of converging ability of the lens.
Power of lens is the reciprocal of focal length. Power =‌

1

f

=‌

100

20

=5D
Therefore, power of convex lens with 20‌cm focal length is +5D.