Give the step-by-step reasoning process and then the final answer. Amanda’s garden contains 20 flowers and Peter’s garden contains three times as many flowers as Amanda's. If Peter gave 15 flowers to his brother, how many flowers are left in his garden?
The number of flowers in Peter’s garden is 20 * 3 = 60 flowers. The number of flowers left after he gave his brother 15 flowers is 60 – 15 = 45 flowers.
The final answer: 45.