The length of a rectangle exceeds its breadth by 4cm. If the length were halved and the breath decreased by 55cm. find the length of the rectangle.

i don't know exactly were to start with this,

the equation i came up with is $\displaystyle \frac{x+4}{2} (x-5) = (x+4)(x) - 55 $

is this right? if it is than i just need to solve for x. But I am unsure weather my equation is correct.