To calculate the power of lens we use the formula:

\(\rm P \) = $\frac{1}{f}$

where \(\rm P\) = Power of lens

and,   \(\rm f\) = focal length of lens

For f= 25cm = 0.25m :

\(\rm P \) = $\frac{1}{f}$

\(\rm or,\) \(\rm P\) = $\frac{1}{0.25}$

\(\rm or,\) \(\rm P \) = \(\rm 4\)

Hence, for lens with focal length 25cm power of lens is +4D.