Energy in an Oscillating Spring?

A 1.15 kg mass on a spring oscillates horizontal frictionless surface. The motion of the mass is described by the equation: x = 0.37cos(3.39t).

In the equation, x is measured in meters and t in seconds. What is the maximum energy stored in the spring during an oscillation?
(in J)
Update: Please provide an explanation for your equations to help me learn! Thank you.
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