If the discount is 30%, we can find the discounted price by taking 70% of the original price (since 100% - 30% = 70%). Substitute the equivalent 0.70 to calculate the discount price: 0.70($24.50) = $17.15. This is the discounted price.
The final cost is $17.15 times 1.07, which includes the discounted price plus the 7% tax. That final cost is 1.07($17.15) = $18.35.
I'm not sure what some of the ordered pairs are in what you wrote, but a function is when each input has one output. So, for every x there is one y. The x values can not repeat. So, remove one of two ordered pairs where the x value is repeating.
