42 IS 21% OF WHAT NUMBER

The problem wants us to find the number that the 21% is 42.
42 is the 21% of 200
How:
=> 21% = 21 /100
=>.21

In order to get the answer we need to find a number to be multiplied by. 21 and get 42 as result.
=> 50 x. 21 = 10.5
=> 100 x. 21 = 21
=> 150 x. 21 = 31.5
=> 200 x. 21 = 42
thus, 42 is the 21% of 200.

For this case we can make use of the following rule of three:

42 -> 21%

x -> 100%

In this case we have the following variable

x: unknown number whose 21% is equal to 42-

From the rule of three we clear x.

We have then:

$$x = (\frac{100}{21}) * (42)\\x = 200$$