Answer:
(n +54)/9 = 21; 135= n
Explanation:
(n+54)/9 = 21
n+54/9 *9= 21*9
n+54-54 = 189-54
n= 135
the first part is simply recognizing the order its written and the words used.
So to start off with, they use the turn "a number" so we know there's going to be some form of a variable. From there it says "increased by" rather than "multiplied" or "doubled" or something of that nature, so we know its adding 54 rather than multiplying. Then, the next part says that "the sum" which is another key term for addition, "is then divided by 9". So we can assume so far that a variable plus 54 is added together to get a number, which is then going to be taken and divided by 9. The last part says "the result is 21", which simply means that we need to end up with 21.
So once we gather all this information, we can put it together as so: (n +54)/ 9 = 21.
I put parentheses around the n + 54 to make sure that the equation is following the system of equations (PEMDAS).