Not understanding how to write algorithms correctly

Question

I have gone through the overview and basic of javascript. Yet for some reason I am having an issues when I try to write a simple algorithm. Not sure what isn't clicking for me.

Answer 1

For instance I'm trying to write code for an algorithm that multiplies price of any given item, quantity of any given item, and the sales price. Where 'price' and 'quantity' are my two undefined variables. My 'salesTax' variable I want to be .10. I want to use these to find my 'totalPrice' variable. I have written this several ways and it isn't coming out right?