Let 
be the unknown number. So, three times that number means 
, and the square of the number is 
We have to sum 528 and three times the number, so we have 
Then, we have to subtract this number from , so we have
The result is 120, so the equation is
This is a quadratic equation, i.e. an equation like 
. These equation can be solved - assuming they have a solution - with the following formula
If you plug the values from your equation, you have
So, the two solutions would be
But we know that x is positive, so we only accept the solution 
Answer:
Because 3(5x) is the same as 3 *5 * x
Step-by-step explanation:
When a number is next to another in parantheses, it signifies multiplication. In this case, we already have 5 and x grouped together by a multiplication sign, so the entire thing is 5 * x. The statement below is key
Distribution in multiplication is only possible if a variable is grouped to another real number by a plus or minus sign.
So in this case, we have 3 * 5 * x, which is 15x. However, if we had 3(5 + x), we would have 15 (3 * 5) + 3x (3 * x).
Hopefully that makes sense!
The answer is C let me know if it was wrong but it should be correct :)
