2. $350
3a: 15 is half of 30, so knowing that means the answer is 50%
3b. 3 is 1/4 of 12 because 3x4 is 12, meaning that 3 is 25% of 12.
3c. 6 over 10 as a decimal is 0.6. Which as a percent is 60%
4. Noah's method does work because 20% x 5 is equal to 100% of a number.
