Energy and Power Questions

The potential energy of a long spring when stretched by $2\text{cm}$ is $U$. If the spring is stretched by $8\text{cm}$ the potential energy stored in it is :

A body of mass $3\text{kg}$ is under a constant force which causes a displacement $s$ in metres in it, given by the relation $s=\frac{1}{3}{t}^2$, where $t$ is in sec. Work done by the force in $2\text{sec}$ is :

$300\text{J}$ of work is done in sliding a $2\text{kg}$ block up an inclined plane of height $10\text{m}$. Taking $g=10{\text{m/s}}^2$, work done against friction is :