#### Answer

The energy stored in the spring will be 18 J

#### Work Step by Step

The energy stored in a spring is $\frac{1}{2}kx^2$, where $k$ is the spring constant and $x$ is the stretch distance.
$\frac{1}{2}kx^2 = 2.0~J$
Let's suppose the spring is stretched a distance of $3x$. We can find the energy $E$ stored in the spring.
$E = \frac{1}{2}k(3x)^2$
$E = 9\times ~\frac{1}{2}kx^2$
$E = (9)(2.0~J)$
$E = 18~J$
The energy stored in the spring will be 18 J.