Heads or tails

If $x$ is the expected number of tosses it takes to get four tails in a row, and the probability of tossing a tails is $\dfrac{1}{4}$ , then we can form the equation

$x=\dfrac{3}{4}(x+1)+\dfrac{3}{16}(x+2)+\dfrac{3}{64}(x+3)+\dfrac{3}{256}(x+4)+\dfrac{1}{64}$

$\Longrightarrow x=\boxed{340}$ .