Tyrosine is an amino acid with the following structure:
The structure contains:
A benzene ring (6 carbon atoms),
A carbon atom in the side chain connected to NH$_2$ and COOH,
Two additional carbon atoms in the COOH and CH$_2$OH groups.
Total carbon atoms = 9.
The motion of an airplane is represented by the velocity-time graph as shown below. The distance covered by the airplane in the first 30.5 seconds is km.
The number of 6-letter words, with or without meaning, that can be formed using the letters of the word MATHS such that any letter that appears in the word must appear at least twice, is $ 4 \_\_\_\_\_$.