Create a function file named PriceCalc that calculates the total price of an order of pens

by doing the following:

$1.$ Takes an integer as an input and outputs the total price of the order by doing

$($number of pens$)*($price of each pen$).$

$2.$ If the input is negative $($ie$.$ negative number of pens$),$ print out a message $$The

number of pens is invalid$$ and set the value for the price as $-1.$

$1$

$3.$ If the input is between $1$ and $20,$ the price of each pen is $$4\mathrm{.}99.$

$4.$ If the input is between $21$ and $50,$ the price of each pen is $$3\mathrm{.}50.$

$5.$ If the input is larger than $50,$ print out a message $$Order too big. Contact

wholesaler$$ and set the total price as $-1.$

Then, in the main script, use the function PriceCalc to find the cost to order $-20$ pens,

$19$ pens, $32$ pens, and $124$ pens