Answer:
42 cm
Explanation:
For a converging lens, the focal length is positive:
f = +14 cm
In this problem, the distance of the object from the lens is 21 cm:
p = +21 cm
The distance of the image from the lens can be found by using the lens equation:
[tex]\frac{1}{f}=\frac{1}{p}+\frac{1}{q}[/tex]
where q is the image distance. Solving the formula for q and substituting the numbers, we find
[tex]\frac{1}{q}=\frac{1}{f}-\frac{1}{p}=\frac{1}{14 cm}-\frac{1}{21 cm}=\frac{1}{42 cm}\\q= 42 cm[/tex]
