Question 658304
DEFINING ONE VARIABLE:
Let one of the numbers be {{{x}}}.
 
THE OTHER NUMBER:
The other number would be {{{25-x}}} because the sum of the two numbers is {{{25}}}.
Since you were asked to "define a variable," I assume that you are expected to use only one variable, and that saying that the other number is {{{25-x}}} should be good enough.
If someone asked for proof of that, you could call the other number {{{y}}}, write that {{{x+y=25}}} and then solve for {{{y}}} to get that {{{y=25-x}}}.
 
TRANSLATING THE OTHER PIECE OF INFORMATION:
"Twelve less than four times one of the numbers is 16 more than twice the other number" talks about "one of the numbers" and "the other number."
Which of those numbers to call {{{x}}} is your choice.
I guess that choice is part of defining your variable.
The choice will determine the equation you end up with, but the end result will be the same.
You could chose to call the first number mentioned {{{x}}}.
In that case,
four times one of the numbers is {{{4x}}}, and
twelve less than that is {{{4x-12}}}.
The other number is {{{25-x}}}.
Twice the other number is {{{2(25-x)}}}, and
16 more than that is {{{2(25-x)+16}}}.
"Twelve less than four times one of the numbers is 16 more than twice the other number" translates as
{{{4x-12=2(25-x)+16}}}.
 
SOLVING THE EQUATION:
{{{4x-12=2(25-x)+16}}} --> {{{4x-12=2*25-2x+16}}} (applying the distributive property)
{{{4x-12=2*25-2x+16}}} --> {{{4x-12=50-2x+16}}} --> {{{4x-12=66-2x}}} (performing indicated operations, collecting like terms)
{{{4x-12=66-2x}}} --> {{{4x-12+12=66-2x+12}}} --> {{{4x=78-2x}}}
{{{4x=78-2x}}} --> {{{4x+2x=78-2x+2x}}} --> {{{6x=78}}}
{{{6x=78}}} --> {{{6x/6=78/6}}} --> {{{highlight(x=13)}}}
The other number is {{{25-13=highlight(12)}}}
 
VERIFICATION:
{{{12+13=25}}}
{{{4*13-12=2*12+16}}} because
{{{4*13-12=52-12=40}}} and {{{2*12+16=24+16=40}}}