Take, for example, the phrase a lot. And yes, I said phrase because a lot is two words, not one. Yet spoken English provides no distinction between one word or two words. That's part of why understanding the distinction between written English and spoken English is so important.
Observing the example sentence in the graphic above, here is the corrected sentence:
For example, the writer can choose a word like many. The sentence would then read as follows:
Due to improper manufacture, seven of the ten support units failed in low-cycle fatigue.
However, when using the phrase a lot, just remember that two words are a lot more than one. Then you'll get the spelling of that phrase correct if not the usage.