For this case we can make the following rule of three:
21 ------> 70%
x --------> 100%
Clearing x we have:
x = (100/70) * (21)
Rewriting we have:
x = (10/7) * (21)
x = 30
Thus,
21 is 70% of 30
Answer:
21 is 70% of 30
If we factorize the expression

We will get

Hope I helped!
The answer is D. 100%
Markup is the amount added to the total cost of product to cover the total overheads and profit.
In markup based on selling price method, the selling price is considered as the endpoint that companies wanted to achieve, (100%) and the markup will be adjusted to cater into thaat equation.