For glasses

Write the lens equation.

\(\frac{1}{v}-\frac{1}{u}=\frac{1}{f}\)

Substitute the values as,

\(\frac{1}{-x}-\frac{1}{\infty}=\frac{1}{f}\)

\(f=-x \operatorname{cm}\)

\(=-\frac{ x }{100}\)

The expression of power is given by,

Power \(=\frac{1}{ f }\)

Therefore,

Power \(=-\frac{100}{ x }\)

\(-5=-\frac{100}{x}\)

\(x =20 cm\)

If he used contact lens,

Consider the following figure.

Here,

\(v =-\infty,\) and \(u =-22 cm\)

Therefore,

\(-\frac{1}{\infty}-\frac{1}{-22}=\frac{1}{ f }\)

\(f =22\)

Therefore, power will be as,

\(p ^{\prime}=-\frac{100}{22} D\)

\(=-4.54 D\)