What do you need to know to find the area abcd ?

You need to know the width and lengthy

Can you show me a picture, I need to know what shape and problem it is

Lets write equation of a function:

y = kx + n

Direct variation in simple is equation of a line which has n=0 or in other words which y to x ratio is k.

First option gets 7=7 but it isnt direct variation because n is not equal to 0

third option is indeed correct. once we implement coordinates (2,7) we get 7=7

Answer is 
y = 7/2x