Answer:
option D
Step-by-step explanation:
Jerry solved this equation:

In the first step , she multiplied 3 inside the parenthesis
1. 
In step 2, 3/4 is added on both sides
2. 
In step 3, we take LCD 12
3. 
In step 4, add the fractions
4. 
Here, 3 or 3/1 are same.

In step 5, to remove 3/1 we multiply both sides by 1/3.
Instead of multiplying 1/3 , Jerry made an error by multiplying 3/1


In step 5, he should have multiplied both sides by 1/3
<span>If logc81=2 then c=9
</span>
5x-2=3x+8
X=5
That's your answer
We can use ratios and the cross-multiply-divide to find this.
The ratio 21:5 is avaliable via the question. We then need to compare that to the ratio x:100, the 100 being the percent and the x being the number of airplane parts.
21/5 = x/100
We can then solve for x to find the number of airplane parts. First we multiply by 100 on both sides to get 2100/5 = x. Therefore x = 420 and there are 420 airplane parts.