The Nueva School - Math Challenge 2

Math Challenge 2

The arrangement ^a _c ^b means a + b - c. For example, ⁴ ₆ ⁵ means 4 + 5 - 6 = 3. Express ⁹ ₅ ⁷ in simplest form.
Karen used to receive $1.50 allowance each week. One week her parents doubled her allowance. The next week they increased the new amount by $1.50. Then the next week they cut this new amount in half. Poor Karen. Karen's allowance is now _____.
If 6 + a = 14 - a, what does a equal?
A whole pizza costs $6.50. Each additional slice of pizza costs $1.25. Harold bought 2 whole pizzas and 2 additional slices. He paid for the pizza with a $20 bill. Harold's change was _____.