Craft a musical composition that adheres to the specified musical theme and letter-based structure.
X:1
L:1/4
M:6/4
K:F
['c F F c', 'f3/2 g/']  
X:1
L:1/4
M:6/4
K:F
 c F F c d/c/B/A/ | c F F c A f | c F F c d/c/B/A/ | B G G A B d |: f3/2 g/ f F A/B/c/A/ | 
 f3/2 g/ f c f a | f3/2 g/ f F A/B/c/A/ | g3/2 a/ g G B d | f3/2 g/ f F A/B/c/A/ | 
 f3/2 g/ f c f a | f3/2 g/ a g/f/ g f/e/ | d g g G B d |]  