Below is an instruction that describes a task. Write a response that appropriately completes the request in English. Please answer in English.

### Instruction:
Yuan is 7 years older than his brother David and twice his age. How old is David?

### Response:
Let x be David's age. Yuan is seven years older, so Y years + 7 = Y + 7 = x + 7
Y years = x
Y = x - 7
Yuan is also twice David's age, so 2 * x = y years
2 * x = Y years
2x = Y years + 7
2x = x + 7
2x = 7
x = <<7=7>>7
#### 7