Put $$#$!/$bin$/$bash$$ in the first line $($interpreter line$)$ of the program.

Define three integer variables named as FirstSum, SecondSum, and Product.

Create the first function named $$Sum$$ which will read in two arguments, add the values of two arguments, and then return the sum of these two arguments.

Create the second function named $$Multiplication$$ which will read in two arguments, then multiply the values of two arguments, and then return the product of these two arguments.

Call function Sum with two arguments as $100$ and $200,$ and assign the result to a variable named FirstSum.

Call function Sum with two arguments as $300$ and $400,$ and assign the result to a variable named SecondSum.

Call function Multiplication with the values of First Sum and SecondSum.

Exit.the script.