Each straw is 4-1/8 inches long.
You have one gigantic piece of straw material, 123-3/4 inches long.
How many straws can you cut it up to make ?
===> (123-3/4) divided by (4-1/8) straws.
Each one costs $0.015 to make.
So, once you find the number of short straws you have,
multiply
===> (the number of short straws) x ($0.015) .
That'll tell you how much it costs to make all of them.
Now you know how to do it on your own.
If you don't get 30 straws and $0.45 , please try again.