This is the sum, I worked it out but got stuck -

Write down a relevant equation involving the variables defined and solve -

The Perimeter of aa Square is $\displaystyle (2x+7) cm$. Its Area is $\displaystyle 49 cm^2$

I worked out an equation and I do get an answer but the answer is negative. The book says the answer should be 10.5 I get -10.5

Here is the Equation:

$\displaystyle (\frac{2x+7}{4})^2=49$

What am I doing wrong?