To get the answer for this question is to:
Divide 56 by 72 = 0.777777778 because 0.777777778 * 72 = 56 cm.
Since 72 cm is related to the side length of 9 cm, take 0.777777778 and multiply it by 9 and you will get 7 for the missing side length.
To get the value of X for the equation to equal 7, take the 7 you got for the missing side length and add it to 20 to get 27 (20 + 7 = 27). Then, take the 27 and divide it by the 3, and you will get 9 for X.
Example:
7 + 20 = 27
27 / 3 = X
9 = 9
&
3x - 20
= 3(9) - 20
= 27 - 20
= 7
The correct answer for the value of X is: 9
Hope this helps!
~ ShadowXReaper069