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

### Instruction:
 汤姆和德文一共教了70年。德文教了比汤姆少5年的一半。汤姆教了多少年？


### Response:
 设x为汤姆教了的年数
德文教了(1/2)x-5年
70 = x + (1/2)x - 5
70 = (3/2)x - 5
75 = (3/2)x
x = <<50=50>>50
汤姆教了50年