Need your help friends..
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Simplify (a/b - b/a) times (a - a^2/a+b) a - a^2/a=b is a mixed number

What is the quadric regression equation that fits these data

Jada has a meal in a restaurant she adds up the prices listed on the menu for everything they ordered and gets a subtotal of $42.00. when the check comes, it says they also need to pay $3.99 in sales tax. what percentage of the subtotal is the sales tax