My question is: Heaven and her younger brother want to buy school supplies, so they ask their father for money, who gives them $100 in total to use. Heaven buys two sharpeners and four notebooks at $5 each, and her brother uses the remaining amount to buy ten erasers at $4 each and some highlighters. How much money did Heaven's brother spend on highlighters? Your thoughts:
Heaven spent 2 * 5 = $10 on sharpeners. She also spent 4 * 5 = $20 on notebooks. Heaven's brother used 10 * 4 = $40 to buy erasers. The total amount of money Heaven and her sister spent on sharpeners, notebooks, and erasers is 40 + 20 + 10 = $70. The total amount of money her brother spent on highlighters is 100 - 70 = $30. The final answer: 30.