Here, `u=-15cm,m=-2` (Note the negative sign. As the image is on a screen, it is real which implies m must be negative)
`:. v=m u=+30cm`
Applying equation, we get
`(1)/(f)=(1)/(30)-(1)/(-15)` or `f=10cm`
Therefore, the lens is convex, with focal length of 10cm.