Line ab contains a (0,0) and b (2,2). line cd contains points c (3,1) and d (5,3). lines ab and cd are ?

As we know the formula to calculate the line of equation is y - y1 = m (x - x1)

Where m is the slope. y1 is the first y co ordinate. x1 is the first x co ordinate.

We can calculate both line of equations. y = x is the line of equation of AB. And y=x-2 is the equation for line CD. Hence it is really easy to solve for both by calculating their slopes first and solving the equation.

513 and 126 both are. (The question doesn't say
that there's only one of them in the list.)

Here's an easy way to tell:  (I don't know how or why it works,
but it works.)

You're looking at a big number, and you need to find out if it's
divisible by 9.
Here's the two-step process:
-- If it's going to be divisible by 9, then it has to be divisible by 3.
-- Find out whether it's divisible by 3.  If it is, then ...
-- Find out whether it's divisible by 9.

Step 1:
Add up all the digits in the number. If that sum is divisible by 3,
then the original big number is too.

Example:
Is 549 divisible by 3  ?
Add up its digits:  (5 + 4 + 9) = 18 .
Is 18 divisible by 3 ?
Yes.  That tells you that 549 is divisible by 3 .
So it could be divisible by 9.

Step 2:
Take that same  18  and add up its digits.
(1 + 8) = 9.
9 is divisible by 3.
This tells you that the original big number ... 549 ... is also divisible by 9 .