C, add the 5 in X and it still equals 12
Let's call the two numbers x and y. The first sentence, one is 6 less than twice another, translates to

We also know the sum of their squares:

So, we have the following system:

We can use the expression for x in terms of y from the first equation to turn the second equation into something involving y alone:

Expand the square:

Subtract 680 from both sides:

Using the quadratic equation

we find the two solutions

Since we know that both numbers are integer we can only accept the second solution. It yields the following x value:

Answer:
X is 160. because you can add all the value of x. But first substrate 540 with 100 which is 440. then 1/2x + 1/2x+ (x-15) + (x-25) which is further simplified as x + 2x - 40. then it's further simplified as 3x - 40 = 440. then add 40 with 440 which is 480 then divide it by 3 which is 160. therefore X= 160.