Answer:
15cm
Explanation:
Since the lens is a diverging lens, the image distance is negative (virtual)
v = -30cm
u = 10cm
Required
focal length f
Using the lens formula;
1/u + 1/v = 1/u
1/10 - 1/30 = 1/f
(3-1)/30 = 1/f
2/30 = 1/f
f = 30/2
f = 15cm
Hence the focal length of the lens is 15cm
