The output of our factory is now three times what it was three years ago.为什么用what

今年我们工厂的产量是三年前的三倍。WHAT 指the output of our factory

当然用what了。
另一种方法： The output of our factory is now three times that of three years ago.= 这里的that of 可换成 what it was

现在我们工厂的产量是三年前的三倍。
“…times+what+从句”是倍数表达的常规句型中变换中的一种。
The production is now three times what it was ten years ago.
类似还有其它句型：
1.…times+more+名词（可数，不可数）+than…
There are five times more books in our library than in
yours.我们图书馆里的书比你们图书馆里的书多五倍。
We have produced twice more grain this year than we did last
year.
我们今年生产的粮食是去年的两倍。
2.
…times as many/much+名词+as…
There is four times as much water in this pot as in that one.
There are six times as many students as we expected.
3.
…times over+被比对象，表示“增加……倍”
The grain output in that village is twice over that of 2002.
4.
…times+that of+被比对象，表示“是……倍”
In this workshop
，the output of July was 4.5 times that of January.

5.
…times+compared with+被比对象
The number of the students in our school has increased 4 times
compared with 1980.我们学校的学生人数比1980年增加了三倍

我们厂今年的产出是三年前产出的三倍。
what这里指三年前的产出数。

it was （what即产量）three years ago