As we know that :
[tex]\begin{gathered}\large{\boxed{\sf{P \: = \: \dfrac{1}{f}}}} \\ \\ \rightarrow {\sf{P \: = \: \dfrac{1}{-25}}}\end{gathered}[/tex]
Power, is in Meter. So divide focal length by 100
[tex]\begin{gathered}\rightarrow {\sf{P \: = \: \dfrac{1}{\dfrac{-25}{100}}}} \\ \\ \rightarrow {\sf{P \: = \: \dfrac{-100}{25}}} \\ \\ \rightarrow {\sf{P \: = \:- 4}} \\ \\ \underline{\sf{\therefore \: Power \: of \: Concave \: lens \: is \: - \: 4D}}\end{gathered}[/tex]
