# Make a strongarm stronger

One of the most lethal NERF guns is the Strongarm, a 6 shooter revolver known for its rapid fire. The firing mechanism is straightforward, a spring is used to drive air through a cylinder which then forces the dart out of the barrel.

Its popularity is due in part to the ease with which it can be modified to shoot faster and farther. One easy modification is to insert a secondary spring inside the main spring, as shown below:

If the strength (spring constant) of the first spring is $$k$$, and the strength of the second spring is $$\frac12 k$$, what is the strength of the two springs together?

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