#10 is much more difficult than #11. You have to translate the words into a usable equation form and then fill in what you know. "What percentage" is "x%", "of the cost of Thad's order" is going to be the dollar amount that paid for the order without delivery fees and those 2 things are multiplied because the word "of" means to multiply, "was used" is "=", "to calculate the delivery fee" is the dollar amount for the delivery fee. Your equation then looks like this: (x%)(149.21-19.46)=19.46 which is (x%)(129.75)=19.46. Divide both sides by 129.75 to get that x = .14998. Multiply by 100 to get the percent: 15%. The second one is easier, you need to set up 2 equations based on the info you're given. 21 waters and 25 cookies cost Thad 45, so that's the first equation. 21w + 25c = 45. If one water and one cookie cost 2, then w + c = 2 is the second equation. Solve the second equation for either w or c. Let's pick w: w = 2 - c and sub it in for the w in the first equation: 21(2-c)+25c=45. Distribute and combine like terms to simplify down to 4c = 3. Divide by 4 to get that a cookie costs 3/4 of a dollar, or 75 cents. Subtract that from 2 to get the cost of a water, which is $1.25.
