Find the percentage increase in y

[topsyturvy]

y is directly proportional to x2.
x is increased by 100%.
Find the percentage increase in y.

so,
y=k x2

y= k (100 + x2)
then i went to find the k,
which is
k= y/ (100 + x2)

so i put back the k which i found into y= k (100 + x2)
which is :
y= y/(100 + x2) (100 + x2)

them I am stuck here..
somebody pls helppp!
thanks lotsa.

 

[courtrigrad]

it should be $$4x^{2}$$ not $$x^{2} + 100$$

 

[VietDao29]

y is directly proportional to x2.
x is increased by 100%.
...
y= k (100 + x2)

x is increased by 100% just means that x has been doubled (i.e: 2x), and not 100 + x. Do you see why?
Consider the original amount (say b) to be 100%, so when increasing the original amount (i.e increase b) by 100% means that you add one more b to your original b, and get 2b, right?
So, can you go from here? :)
-------------
@courtrigrad: No, it should be 4x², not 2x².
EDIT: He did edit the post. Cheers. :)