Question

please do the followig sum

Answer 1

hope it helps. all the best.

Answer 2

$\frac{1 }{f} = \frac{1}{25} + ( \frac{1}{- 75} ) \\ f = \frac{75}{2} \\ now \: \frac{100}{f} = p \\ therefore. \\ \frac{100}{ \frac{75}{2} } = p \\ p = 2.6d$