Parallel lines have the exact same slope ( or else they would eventually run into each other). So the answer is -1/2 is the slope.
We have 3⁴ = 81, so we can factorize this as a difference of squares twice:
Depending on the precise definition of "completely" in this context, you can go a bit further and factorize 
as yet another difference of squares:
And if you're working over the field of complex numbers, you can go even further. For instance,
But I think you'd be fine stopping at the first result,
STEP 1:
determine equations needed
x= # of $10 tickets
y= # of $14 tickets
QUANTITY EQUATION
x + y= 800
COST EQUATION
$10x + $14y= $9,040
STEP 2:
multiply quantity equation by -14
-14(x + y)= -14(800)
-14x - 14y= -11,200
STEP 3:
add new quantity equation in step 2 to cost equation of step 1 to solve for x using elimination
-14x - 14y= -11,200
10x + 14y= 9040
y term cancels out
-4x= -2160
divide both sides by -4
x= 540 ten dollar tickets
STEP 4:
substitute x value in step 3 into either original equation
x + y= 800
540 + y= 800
subtract 540 from both sides
y= 260 fourteen dollar tickets
ANSWER: There were 540 $10 tickets and 260 $14 tickets sold.
Hope this helps! :)
4y - 1 = 7 / + 1 ;
4y = 8 /÷4 ;
y = 2 ;
