The tension in the spring is proportional to the extension. When the extension is 3 inches, tension = weight of body = mg. So when extension = 7 inches, tension = . So, if we resolve vertically at the point of maximum extension:
, taking g = 32
With the usual notation, the equation of motion is
And we know that when feet, . So we can now work out the value of
Now the velocity, displacement and amplitude are related by
The maximum velocity is when . So max velocity = . And the time it takes to reach its highest point is half the period of a complete oscillation. And that period is
Can you take it from here?