what do i do???

https://www.mathsisfun.com/algebra/factoring-quadratics.html

x^2-4x=11

First you take away the 11 so you have a quadratic.

x^2-4x-11=0

Now you factorise.

Since 11 is a prime number we shall have to use the quadratic equation:

a=1

b=-4

c=-11

Your two possible solutions are:

x=5.87....

or 

x=-1.87....

You can use the Quadratic Formula as previously illustrated.    You can also 'complete the square'

Take 1/2 of the 'x' coefficient, square itn and add it to both sides:

x^2 -4x + (-2^2) = 11 + (-2^2)

x^2 -4x +4 = 15

(x-2)^2 = 15         Now take the sqrt of both sides

x-2 = +- sqrt15

x = 2 + or - sqrt15        (same answers as Quadratic Formula)