Question 19193
Hint: When you want to show the square root of a quantity, enclose that quantity in parentheses, thus: Square root(4x^2+x-3) = 2x

Now to your problem:

{{{sqrt(4x^2+x-3) = 2x}}} Square both sides.
{{{4x^2+x-3 = 4x^2}}} Subtract 4x^2 from both sides.
{{{x-3 = 0}}} Add 3 to both sides.
{{{x = 3}}}