Write a function that will return the square root of a number if it is not negative, otherwise return None. Test it with the following numbers: $5,0,-3.$

b$.$ Write a lambda function that takes quantity, price and tax as decimal value $(0\mathrm{.}05$ for $5\%)$ as input and returns sale amount including tax. Test it with quantity $=100,$ price $=$$$1\mathrm{.}50$ and tax $=7\mathrm{.}5\%$