the wings of the plane,which stretched out for 80 feet,were

倍数表示法
1.主语+谓语+倍数（或分数）+ as + adj.+ as
I have three times as many as you.我有你三倍那么多.
2.主语+谓语+倍数（分数）+ the size (amount,length…) of…
The earth is 49 times the size of the moon.地球是月球的49倍.
3.主语+谓语+倍数（分数）+ 形容词（副词）比较级+ than…
The grain output is 8 percent higher this year than that of last year.
今年比去年粮食产量增加8%.
4.还可以用by+倍数,表示增加多少倍
The production of grain has been increased by four times this year.
今年粮食产量增加了4倍
这道题是第二种情况

主语+谓语+倍数